Mind: A Brief Introduction (John R. Searle)

Now what exactly are these assumptions and why are they false? I cannot tell you that just yet. They do not admit of a quick summary without some preliminary work. The first half of this book is in large part about exposing and overcoming those assumptions. It is hard to summarize them because we lack a neutral vocabulary in which to describe mental phenomena. So I have to begin by appealing to your experiences.

So far you have had three types of conscious experiences: thinking about something, intentionally doing something, and feeling a sensation. What is the problem? Well, now look at the objects around you, the chairs and tables, houses and trees. These objects are not in any sense “subjective.” They exist entirely independent of whether or not they are experienced. Furthermore, we know independently that they are entirely made of the particles described by atomic physics, and that there is no qualitative feel to being a physical particle, or for that matter being a table.

Now this simple contrast between our experiences and the world that exists independently of our experiences invites a characterization, and in our traditional vocabulary the most natural characterization is to say is that there is a distinction between the mental, on the one hand, and the physical or material, on the other. The mental qua mental is not physical. And the physical qua physical is not mental. It is this simple picture that leads to many of the problems, and our three harmless-looking examples exemplify three of the worst problems.

People who accept the reality and irreducibility of the mental tend to think of themselves as dualists. But to others, accepting an irreducible mental component in reality seems like giving up on the scientific world-view, so they deny the existence of any such mental reality. They think it can all be reduced to the material or eliminated altogether. They tend to think of themselves as materialists. I think both sides are making the same mistake. I am going to try to overcome the vocabulary and the assumptions, and in so doing I am going to try to solve or dissolve the traditional problems. But once we do that, the subject, the philosophy of mind, does not end: it gets more interesting. And this is my second reason for wanting to write this book.

There are two distinctions that I want you to be clear about at the very beginning, because they are essential for the argument and because the failure to understand them has led to massive philosophical confusion. The first is the distinction between those features of a world that are observer independent and those that are observer dependent or observer relative. Think of the things that would exist regardless of what human beings thought or did. Some such things are force, mass, gravitational attraction, the planetary system, photosynthesis, and hydrogen atoms. All of these are observer independent in the sense that their existence does not depend on human attitudes. But there are lots of things that depend for their existence on us and our attitudes. Money, property, government, football games, and cocktail parties are what they are, in large part, because that’s what we think they are. All of these are observer relative or observer dependent. In general, the natural sciences deal with observer-independent phenomena, the social sciences with the observer dependent.

Where the mind is concerned we also need a distinction between original or intrinsic intentionality on the one hand and derived intentionality on the other. For example I have in my head information about how to get to San Jose. I have a set of true beliefs about the way to San Jose. This information and these beliefs in me are examples of original or intrinsic intentionality. The map in front of me also contains information about how to get to San Jose, and it contains symbols and expressions that refer to or are about or represent cities, highways, and the like. But the sense in which the map contains intentionality in the form of information, reference, aboutness, and representations is derived from the original intentionality of the map makers and users. Intrinsically the map is just a sheet of cellulose fibers with ink stains on it. Any intentionality it has is imposed on it by the original intentionality of humans.

I write out of the conviction that the philosophy of mind is the most important subject in contemporary philosophy and that the standard views—dualism, materialism, behaviorism, functionalism, computationalism, eliminativism, epiphenomenalism—are false.

For most of the twentieth century the philosophy of language was “first philosophy.” Other branches of philosophy were seen as derived from the philosophy of language and dependent on results in the philosophy of language for their solution. The center of attention has now moved from language to mind. Why? Well, first, I think many of us working in the philosophy of language see many of the questions of language as special cases of questions about the mind. Our use of language is an expression of our more biologically fundamental mental capacities, and we will not fully understand the functioning of language until we see how it is grounded in our mental abilities. A second reason is that with the growth of knowledge we have seen a movement away from treating the theory of knowledge, epistemology, as central in philosophy and we are now prepared to do a more substantive, theoretical, constructive philosophy, rather than just dealing piecemeal with specific traditional problems.

The ideal place to begin that constructive philosophy is to start by examining the nature of the human mind.

A third reason for the centrality of the mind is that, for many of us, myself included, the central question in philosophy at the beginning of the twenty-first century is how to give an account of ourselves as apparently conscious, mindful, free, rational, speaking, social, and political agents in a world that science tells us consists entirely of mindless, meaningless, physical particles. Who are we,…

invention of “cognitive science,” a new discipline that attempts to go deeper into the nature of the mind than was customary in traditional empirical psychology. Cognitive science…

Finally, more controversially, I think the philosophy of language has reached a period of relative stagnation because of certain common mistakes that surround the doctrine of so-called externalism, the idea that the meanings of words, and by extension the contents of our minds, are not inside our heads, but are…

The philosophy of mind has a special feature that distinguishes it from other branches of philosophy. In most philosophical subjects there is no sharp division between what the professionals believe and the opinions of the educated general public. But on the issues discussed in this book, there is an enormous difference between what most people believe and what the professional experts believe. I suppose most people in the Western world today accept some form of dualism. They believe they have both a mind, or a soul, and a body. I have even heard some people tell me they have three parts—a body, a mind, and a soul. But this is definitely not the view of the professionals in philosophy…

In philosophy there is no escaping history. Ideally, I sometimes think, I would just like to tell my students the truth about a question and send them home. But such a totally unhistorical approach tends to produce philosophical superficiality. We have to know how it came about historically that we have the questions we do and what sorts of answers our ancestors gave to these questions.

Cartesian dualism was important in the seventeenth century for a number of reasons, not the least of which being that it seemed to divide up the territory between science and religion. In the seventeenth century the new scientific discoveries seemed to pose a threat to traditional religion and there were terrific disputes about the apparent conflict between faith and reason. Descartes partly, although not entirely, defused this conflict by, in effect, giving the material world to the scientists and the mental world to the theologians. Minds were considered to be immortal souls and not a proper topic of scientific investigations, whereas bodies could be investigated by such sciences as biology, physics, and astronomy. Philosophy, by the way, he thought could study both mind and body.

Each mind is an immortal soul. Bodies, as physical entities, are determined by the laws of physics; but minds have free will. Each of us as a self is identical with his or her mind. As living human beings we are composite entities, comprising both a mind and a body, but for each of us the self, the object referred to by “I,” is a mind that is somehow attached to our body. Gilbert Ryle, a twentieth-century philosopher of mind, sneered at this aspect of Descartes’ view by calling it the doctrine of “the ghost in the machine.” Each of us is a ghost (our mind) inhabiting a machine (our body).2 We know both the existence and the contents of our minds by a kind of immediate awareness, which Descartes summarizes in the most famous sentence of his philosophy, “Cogito ergo sum”: I think therefore I exist. This looks like a formal argument with “I think” as premise and “I exist” as conclusion, but I believe that Descartes intended it also to record a kind of inner inspection of the existence and the contents of the mind. I cannot be mistaken about the existence of my own consciousness, hence I cannot be mistaken about my own existence, because it is my essence to be a conscious (that is, thinking) being, a mind. Nor can I be mistaken about the contents of my mind. If it seems to me, for example, that I have a pain, then I do have a pain.

Bodies, on the other hand, cannot be known directly but only indirectly by inferring their existence and features from the contents of the mind. I do not directly perceive the table in front of me; but, strictly speaking, I perceive only my conscious experience of the table, my “idea” of the table; and I infer the existence of the table from the presence of the idea. My present idea of the table is not caused by me, so I have to assume that it is caused by the table.

What exactly are the relations between the mental and the physical, and in particular how can there be causal relations between them? It seems impossible that there should be causal relations between two completely different metaphysical realms, the physical realm of extended material objects and the mental or spiritual realm of minds or souls. How does anything in the body cause anything in the mind? How does anything in the mind cause anything in the body? Yet, it seems we know that there are causal relations. We know that if somebody steps on my toe, I feel a pain even though his stepping on my toe is just a physical event in the physical world, and my feeling of pain is a mental event that occurs inside my soul. How can such things happen? Just as bad: it seems there are causal relations going the other way as well. I decide to raise my arm, an event that occurs inside my conscious soul, and, lo and behold, my arm goes up. How are we supposed to think that such a thing could ever happen? How can a decision in my soul cause a movement of a physical object in the world such as my body? This is the most famous problem that Descartes left us, and it is usually called the “mind-body problem.” How can there be causal relations between the two? Much of the philosophy of mind after Descartes is concerned with this problem, and it is still, in spite of all of our progress over the centuries, a leading problem in contemporary philosophy.

The problem for Descartes was not the general question of how a mental substance can arise out of neurobiology, because for him it cannot. His question was rather how specific mental contents such as feeling a pain can arise from the impact of an injury to my body. We think the very existence of a mind is explained by the operations of the brain. Descartes did not think that was possible. For him the question was only how specific thoughts and feelings, such as a sensation of pain, can be caused by events occurring to the body. It is important to emphasize this point: we tend to think, even the dualists among us, that our bodies with their brains are conscious. Descartes did not think that. He thought bodies and brains could no more be conscious than tables or chairs or houses, or any other hunk of junk. Conscious souls are separate, though somehow attached to human bodies. But no material object, living or dead, is conscious.

The view that I am the only person who has mental states is called “solipsism.” Solipsism comes in at least three different grades. One, the most extreme form: I am the only person in the world who has mental states; and indeed in some forms, nothing exists in the world except my mental states. Two, epistemic solipsism: maybe other people have mental states, but I can never know for sure. It is quite possible that they do but I have no way of finding out, because all I can observe is their external behavior. And three: Other people do have mental states, but I can never be sure that they are like mine. For all I know, what I call “seeing red,” if you could have that very experience you might call it “seeing green,” and if I could have your experience that you call “seeing red” I would call it “seeing green.” We both pass the same color blindness tests because we both make the same discriminations in our behavior. If asked to pick out the green pencil from a box of red pencils, we both pick the same pencil. But how do I know that the inner experiences you have that enable you to discriminate are similar to the ones I have that enable me to discriminate?

The skepticism about other minds that follows from Cartesian dualism is just a special case of a much more general kind of skepticism: skepticism about the existence of the external world.

It is important to understand that on Descartes’ view we do not directly perceive objects and states of affairs in the world. What we directly perceive, that is, perceive without any inferential processes, are the contents of our own minds. So if I hold up my hand in front of my face, what I directly perceive, what I strictly and literally perceive, according to Descartes, is a certain visual experience that I am having. Descartes calls these experiences “ideas.” I perceive not the hand in itself, but rather a certain visual representation of the hand, a kind of mental picture of the hand. But then the question arises, How do I know there really is a hand out there on the other side causing me to have this mental picture?

How do I know that the representation really represents, or represents accurately? Descartes’ view was common in the seventeenth century. It is called the “representative theory of perception,”

Descartes presents very little by way of an argument to show that we cannot directly perceive tables, chairs, mountains, etc. but can only perceive our ideas of these things. He makes the transition from perceiving real objects to perceiving only the contents of our own minds very casually. Though he was by no means the first philosopher to hold this view, the move from the view that we really perceive real objects to the view that we only perceive our ideas of objects is a move of decisive importance in the history of philosophy. Indeed, I would say it is the greatest single disaster in the history of philosophy over the past four centuries. In contemporary jargon, it is put by saying: we do not perceive material objects, we perceive only “sense data.”

Do I genuinely have free will, or is it only an illusion? The question comes in a very sharp form for Descartes, because if my free will is a feature of my mind, how can it have any effect on the physical world, if the physical world is entirely determined? This problem is an extension of, but not the same as, the mind-body problem. For even if we have a solution to the mind-body problem, even if we can show how my thoughts and feelings can move my body, there is still the question, How is this consistent with the conception of physics of Descartes’ time that the physical world is a completely causally closed, deterministic system? Every event that happens in the physical world is determined by preceding physical events. So even if we could prove somehow that we have mental free will, it wouldn’t make any difference to the behavior of my body, because the behavior of my body is caused by the preceding states of my body and the rest of the physical universe. The problem of free will seems difficult for anyone, but it raises exceptional problems for someone who accepts dualism.

But is this body really essential to my identity? It seems at least possible to imagine that I might, like Gregor Samsa in the story by Kafka, wake up in a completely different body. But if the same body is not what makes me me, then what does make me me? What is the relation between my personal identity and my bodily identity? In addition to this or that particular experience, do I also have the experience of myself as a self? The dualist’s answer to these questions is swift. My body has nothing whatsoever to do with my identity. My identity consists entirely in the continuation of the same mental substance, the same soul, or res cogitans. Material objects may come and go and experiences may come and go, but my identity is guaranteed by the sameness of my mental substance, for I am identical with that substance.

If every mind is a spiritual or mental substance, and if minds are indestructible, then it seems that if animals have minds, every animal has an immortal soul. But if it turns out that every dog, cat, mouse, flea, and grasshopper has an immortal soul, then, to put it mildly, heaven is going to be very much overpopulated. Descartes’ solution to the problem of animal minds was swift and brutal. He said that animals do not have minds. He was not at all dogmatic about that; he thought that perhaps they have minds, but it seemed to him scientifically unlikely that they had minds. He thought the crucial distinction between us and animals, that enables us to tell for sure that human beings have minds and animals do not, is that human beings have a language in which they express their thoughts and feelings, and animals have no language. Their lack of language he considered to be overwhelming evidence that they have no thoughts or feelings. Descartes agreed that this is a somewhat counterintuitive result. If we see a dog hit by a carriage and we hear the dog howling in apparent pain, it looks like we have to assume that the dog has feelings just as we do. But Descartes says all of that is an illusion. We should no more pity the dog than we pity the carriage when it is involved in a crash.

“Intentionality” is a technical term used by philosophers to refer to that capacity of the mind by which mental states refer to, or are about, or are of objects and states of affairs in the world other than themselves. So, for example, if I have a belief, it must be a belief that something is the case. If I have a desire, it must be a desire to do something or that something should happen. If I have a perception, I must at least take myself to be perceiving some object or state of affairs in the world. All of these are said to be intentional, in the sense that in each case the state refers beyond itself. Intending, in the ordinary sense in which I intend to go to the movies tonight, is just one kind of intentionality among others along with belief, hope, fear, desire, and perception.

The special philosophical problem of intentionality is this: suppose that I now believe that George W. Bush is in Washington. The question arises, How can my thoughts, which are entirely inside my mind, reach out all the way to Washington, D.C.? If I think the sun is 93 million miles from the earth, how is it, again, that my thoughts can reach out and refer beyond themselves? The problem of how a mental state can refer to or be about something beyond itself is the problem of intentionality.

Some philosophers who think that we could explain how consciousness is caused by brain processes cannot see how consciousness could have any causal powers of its own. Granted that somehow or other consciousness, and mental phenomena generally, are dependent on brain processes, it is hard to see how they could cause bodily movements or cause anything in the physical world. The view that mental states exist but are causally inert is called “epiphenomenalism.” On this view consciousness exists alright, but it is like the froth on the wave or the flash of sunlight reflected off the surface of the water. It is there but it does not really matter. It is an epiphenomenon. But this seems too counterintuitive. Every time I decide to raise my arm, it goes up. And it is not a random or statistical phenomenon. I do not say, “Well, that’s the thing about the old arm. Some days she goes up and some days she doesn’t.” The problem is to show how something not a part of the physical world could have such effects on the physical world.

A large part of this book will be concerned with the 12 problems that I have just outlined. If those problems look interesting to you, you are likely to find this book interesting.

In a famous passage Descartes said we should not think of the mind as lodged in the body like a pilot in a ship, but we should really think that it is somehow suffused throughout the body. If I bump into something I do not observe my body banging into another object in a way that the pilot of a ship might observe the ship banging into the wharf, but rather I feel a pain in the part of my body that comes in contact with the object. Descartes says we should think of our mind as if it were somehow suffused throughout the body, but on his own account, that cannot be a correct thing to say, because mental substance cannot be spatially extended. It cannot be spread throughout the body because it cannot be spread out at all.

According to the argument from analogy, I infer the existence of mental states in other people, by analogy with myself. Just as I observe a correlation of my own behavior with my mental states, so I can infer the presence of appropriate mental states in others when I observe their behavior. I have already pointed out the limitations of this form of argument. The problem is that in general with inferential knowledge there must be some independent check on the inference if the inference is to be valid. Thus for example, I might discover that a container is empty by banging on the container and inferring from the hollow sound that there is nothing in it, but this inferential form of knowledge only makes sense given the assumption that I could open up the container and look inside and thus noninferentially perceive that the container is empty. But in the case of knowledge of other minds there is no noninferential check on my inference from behavior to mental states, no way that I can look inside the container to see if there is something there.

assuming that God exists, he argues that God cannot be a deceiver. Because of God’s perfection, it would be inconsistent to suppose that he could be a deceiver, for deceit is an imperfection. But if God is not a deceiver, then there must exist an external world, and I must have some sort of correct knowledge when I make observations of the external world. Why? Because God gives me every reason to believe, for example, that there is a desk in front of me, and a chair on which I’m sitting, and no reason to suppose otherwise. Therefore, if I am mistaken, God would be deceiving me, and that is impossible. This then raises a problem for Descartes: How is error is possible? And his answer is that error is possible because my will exceeds my understanding. My will is potentially infinite; my understanding is finite. And I often will to believe things that I do not clearly and distinctly perceive to be true, and consequently, I can be mistaken. It is important to emphasize that Descartes did not think that our perceptions are in general accurate representations of the world. Objects do not really have colors, tastes, or smells, nor do they give off sounds, even though colors, tastes,…

Hume made devastating criticisms of the Cartesian account of the self and personal identity. There is no experience of the self, according to Hume; and the identity that we ascribe to ourselves through the changes in our lives is an entirely fictitious identity. It is a kind of systematic illusion. Many other philosophers follow Hume in supposing that there is no such thing as a self in addition to the sequence of our particular experiences. Lichtenberg thought that the “I” in sentences such as “I think” gives us the illusion that there is an “I” that does the thinking; but he says we should say rather “It thinks,” where the “it” is like the “it” in “It’s raining.” It does not actually refer to an entity.

I think the answer is that the basis on which I am confident that my dog is conscious and has a specific content to his consciousness is not simply that his behavior is appropriate, but that I can see that the causal underpinnings of the behavior are relatively similar to mine. He has a brain, a perceptual apparatus, and a bodily structure that are relevantly similar to my own: these are his eyes, these are his ears, this is his skin, there is his mouth. It is not just on the basis of his behavior that I conclude that he is conscious, but rather on the basis of the causal structure that mediates the relation between the input stimulus and the output behavior. In the case of humans, the input stimulus causes experiences, which in turn cause output behavior. The underlying physical structure that enables the input stimulus to cause experiences is relevantly similar in humans and higher animals. For that reason we are completely confident that dogs and chimpanzees have conscious states, in many respects like our own. When it comes to snails and termites, we have to leave it up to the experts to tell us whether or not they have a rich enough neurobiological capacity to have conscious life.

What I have tried to do in this chapter is to present the framework for the discussions that will follow. The problems will not be treated as of equal weight. Not by any means. The next three chapters will be largely devoted to the mind-body problem. I have already said what I will have to say about animals and sleep. Several problems receive a chapter of their own: intentionality, mental causation, free will, the unconscious, perception, and the self. Some of the other problems, though they are of great importance, will receive only rather brief discussion in this book, because they go far beyond the philosophy of mind, especially skepticism and social science explanation.

Because of the failures of Cartesian-style dualism, especially the failure to get an adequate or even coherent account of the relationship between the mind and the body, it is widely assumed that substance dualism in any form is out of the question. This is not to say that no serious professionals are substance dualists. But in my experience most substance dualists I know are people who hold this view for some religious reasons, or as part of a religious faith. It is a consequence of substance dualism that when our body is destroyed our soul can continue to survive; and this makes the view appealing to adherents of religions that believe in an afterlife. But among most of the professionals in the field, substance dualism is not regarded as a serious possibility. A prominent exception is the defense of dualism offered by Karl Popper and J. C. Eccles.1 They claim that there are two quite distinct worlds, World 1 of physical objects and states and World 2 of states of consciousness. Each is a separate and distinct world that interacts with the other. Actually they go Descartes one better and also postulate World 3, a world of “culture in all its manifestations.”

It seems impossible to make substance dualism consistent with modern physics. Physics says that the amount of matter/energy in the universe is constant; but substance dualism seems to imply that there is another kind of energy, mental energy or spiritual energy, that is not fixed by physics. So if substance dualism is true then it seems that one of the most fundamental laws of physics, the law of conservation, must be false. Some substance dualists have attempted to cope with this problem by claiming that for each infusion of spiritual energy, there is a diminution of physical energy, thus preserving a constant amount of energy in the universe. Others have said that the mind rearranges the distribution of energy in the universe without adding to it or subtracting from it. Eccles says that the mind can affect the body by altering the probability of neuronal events without any energy input, and that quantum physics enables us to see how this can be done: “The hypothesis of mind-brain interaction is that mental events act by a quantal probability field to alter the probability of emission of vesicles from presynaptic vesicular grids.”3 There is something ad hoc about these maneuvers, in the sense that the authors are convinced in advance of the truth of dualism and are trying to find some way, any way, that will make dualism consistent with physics.

It is not easy to make the idea that the mind is a separate substance consistent with the rest of what we know about the world. Here are three ways of trying to do it, each with a different conception of the mind. First, divine intervention. Physical science is incomplete. Our souls are something in addition to the rest of the world. They are created by divine intervention and are not part of the physical world as described by science. Second, quantum mechanics. The traditional mind-body problem arises only because of an obsolete Newtonian conception of the physical. On one interpretation of quantum measurement, consciousness is required to complete the collapse of the wave function and thus create quantum particles and events. So some form of consciousness is not created by the rest of nature, rather it is essential for the creation of nature in the first place. It is a primitive part of nature required to explain brain processes and everything else.4 Third, idealism. The universe is entirely mental. What we think of as the physical world is just one of the forms that the underlying mental reality takes.

There is a weaker version of dualism called “property dualism,” and that view is fairly widespread. The idea is this: Though there are not two kinds of substances in the world, there are two kinds of properties. Most properties, such as having an electrical charge, or having a certain mass, are physical properties; but some properties, such as feeling a pain or thinking about Kansas City, are mental properties. It is characteristic of human beings that though they are not composed of two different kinds of substances, their physical bodies, and in particular their brains, have not only physical properties, but mental properties as well. Property dualism avoids postulating a separate mental substance, but it inherits some of the difficulties of substance dualism. What are the relationships between the mental and the physical supposed to be? How is it that physical events can ever cause mental properties?

My guess is that dualism, in spite of being out of fashion, will not go away. Indeed in recent years dualism, at least property dualism, has been making something of a comeback, partly due to a renaissance of interest in consciousness. The insight that drives dualism is powerful. Here is the insight, at its most primitive: we all have real conscious experiences and we know that they are not the same sort of thing as the physical objects around us. This primitive insight can be given a more sophisticated formulation: the world consists almost entirely of physical particles and everything else is in some way an illusion (like colors and tastes) or a surface feature (like solidity and liquidity) that can be reduced to the behavior of the physical particles. At the level of molecular structure the table is not really solid. It is, as the physicist Eddington said, a cloud of molecules. It is just that from our point of view it seems solid. But at bottom the physical world consists entirely of microentities, the physical particles. However there is one exception. Consciousness is not just particles. In fact it is not particles at all. Whatever else it is, it is something “over and above” the particles. I believe this is the insight that drives contemporary property dualism.

The dualists said that there are two kinds of things or properties in the universe, and with the failure of dualism, it is natural to suppose that maybe there is only one kind of thing in the universe. Not surprisingly, this view is called “monism” and it comes in two flavors, mentalist monism and materialist monism. These are called “idealism” and “materialism,” respectively.

The single most influential family of views in the philosophy of mind throughout the twentieth century and leading into the twenty-first century is one version or another of materialism. Materialism is the view that the only reality that exists is material or physical reality, and consequently if mental states have a real existence, they must in some sense be reducible to, they must be nothing but, physical states of some kind. There is a sense in which materialism is the religion of our time, at least among most of the professional experts in the fields of philosophy, psychology, cognitive science, and other disciplines that study the mind. Like more traditional religions, it is accepted without question and it provides the framework within which other questions can be posed, addressed, and answered.

In the next few pages I am going to sketch briefly the history of materialism in the twentieth century, up to the point where it finally reached its most sophisticated formulation in the computational theory of the mind, the theory that the brain is a computer and the mind is a computer program.

The earliest influential form of materialism in the twentieth century was called “behaviorism.” In its crudest version, behaviorism says the mind just is the behavior of the body. There is nothing over and above the behavior of the body that is constitutive of the mental. Behaviorism comes in two flavors, “methodological behaviorism” and “logical behaviorism.”

Methodological behaviorism was a movement in psychology. It attempted to put psychology on a respectable scientific footing, along with other natural sciences, by insisting that psychology should study only objectively observable behavior. The “laws” that such a discipline was supposed to discover were laws that would correlate the input stimulus to the organism with the output response behavior; and for this reason, behaviorist psychology was sometimes called “stimulus-response” psychology. The behaviorists were so influential that for a time they even succeeded in changing the definition of psychology. Psychology was no longer the “science of the mind” but the “science of human behavior.” This view was called “methodological behaviorism” because it proposed a method in psychology rather than a substantive claim about the existence or nonexistence of the mind. The real objection to dualism, the methodological behaviorists claimed, was not that it postulates nonexistent entities, but rather that it is scientifically irrelevant. Scientific claims have to be objectively testable, and the only objectively testable claims about the human mind are claims about human behavior.

According to a typical behaviorist analysis, to say that Jones believes it is going to rain just means the same as saying an indefinite number of statements such as the following: if the windows in Jones’s house are open, he will close them; if the garden tools are left outside, he will put them indoors; if he goes for a walk he will carry an umbrella or wear a raincoat or both; and so forth. The idea was that having a mental state was just being disposed to certain sorts of behavior; and the notion of a disposition was to be analyzed in terms of hypothetical statements, statements of the form “If p then q.” As applied to the problem of mental states, these statements would take the form, “If such-and-such conditions obtain, then such-and-such behavior will ensue.”

Chomsky claimed that the idea that when we study psychology we are studying behavior is as unintelligent as the idea that when we study physics we are studying meter readings. Of course we use behavior as evidence in psychology, just as we use meter readings as evidence in physics, but it is a mistake to confuse the evidence that we have about a subject matter for the subject matter itself. The subject matter of psychology is the human mind, and human behavior is evidence for the existence and features of the mind, but is not itself the mind.

I said earlier that the behaviorists would analyze Jones’s belief that it is going to rain into sets of statements about his rain-avoidance behavior. But the difficulty with that is that we can only begin to make such a reduction on the assumption that Jones desires to stay dry. So the assumption that Jones will carry an umbrella if he believes that it is going to rain is only plausible if we suppose that Jones does not want to be rained on. But then if we are analyzing belief in terms of desire, it looks like there is a kind of circularity in the reduction. We did not really reduce the belief to behavior; we reduced it to behavior plus desire, which still leaves us with a mental state that needs to be analyzed.

The real difficulty with behaviorism, though, is that its sheer implausibility became more and more embarrassing. We do have thoughts and feelings and pains and tickles and itches, but it does not seem reasonable to suppose that these are identical with our behavior or even with our dispositions to behavior. The feeling of pain is one thing, pain behavior is something else. Behaviorism is so intuitively implausible that unsympathetic commentators often made fun of it. As early as the 1920s, I. A. Richards pointed out that to be a behaviorist you have to “feign anesthesia.”9 And university lecturers have a stock repertoire of bad jokes about behaviorism. A typical joke: a behaviorist couple just after making love, he says to her “It was great for you. How was it for me?”

The sheer implausibility of behaviorism had become an embarrassment by the 1960s and it was gradually replaced among materialist-minded philosophers by a doctrine called “physicalism,” sometimes called the “identity theory.” The physicalists said that Descartes was not wrong, as the logical behaviorists had claimed, as a matter of logic, but just as a matter of fact. It might have turned out that we had souls in addition to bodies, but the way that nature in fact turned out, what we think of as minds are just brains, and what we think of as mental states, such as the feeling of pain or having a tickle or an itch, are just states of the brain—and perhaps the rest of the central nervous system. This thesis was sometimes called the “identity thesis” because it asserted an identity between mental states and brain states.

The model for the behaviorists was one of definitional identities. Pains are dispositions to behavior in a way that triangles are three-sided plane figures. In each case it is a matter of definition. The identity theorists said no, the model is not definitions, but rather empirical discoveries of identities in science. We have discovered, as a matter of fact, that a bolt of lightning is identical with an electrical discharge; we have discovered, as a matter of fact, that water is identical with H2O, and we are now discovering, and the discovery is proceeding daily, that mental states are really identical with brain states.

There were a number of objections to the identity theory. I find it useful to distinguish between the technical objections and the common-sense objections. The first technical objection was that the theory seemed to violate a principle of logic called “Leibnitz’s Law.”11 The law says that if any two things are identical, then they must have all their properties in common. So if you could show that mental states had properties that could not be attributed to brain states, and brain states had properties that could not be attributed to mental states, it looks like you would refute the identity theory.

One slightly more technical objection that really did concern the identity theorists and indeed eventually forced a modification in their views was the accusation of “neuronal chauvinism.”16 If the claim of the identity theorists was that every pain is identical with a certain kind of neuronal stimulation, and every belief is identical with a certain type of brain state, then it seems that a being that did not have neurons or that did not have the right kind of neurons could not have pains and beliefs. But why can’t animals that have brain structures different from ours have mental states? And indeed, why couldn’t we build a machine that did not have neurons at all, but also had mental states? This objection led to an important shift in the identity theory from what came to be called “type-type identity theory” to “token-token identity theory.”

In order to explain this distinction I need to say a bit about the type-token distinction. If I write the word “dog” three times: “dog dog dog,” have I written one word or three? Well, I have written three instances, or tokens, of one type of word. So we need a distinction between types, which are abstract general entities, and tokens, which are concrete particular objects and events. A token of a type is a particular concrete exemplification of that abstract general type.

The type-type identity theory says “Every type of mental state is identical with some type of physical state.” By their own lights this is a bit sloppy, because the identity in question is between actual concrete tokens and not abstract universal types. What they meant is: for every mental-state type there is some brain-state type such that every token of the mental type is a token of the brain type. The token identity theorists simply said: for every token of a certain type of mental state, there is some token of some type of physical state or other with which that mental state token is identical. They, in short, did not require, for example, that all token pains had to exemplify exactly the same type of brain state. They might be tokens of different types of brain states even though they were all tokens of the same mental type, pain. For that reason they were called “token-token” identity theorists as opposed to “type-type” identity theorists. Token-token identity seems much more plausible than type-type identity theory.

But now they are faced with an interesting question. What is it that all of these tokens have in common that makes them tokens of the same mental-state type? If you and I both believe that Denver is the capital of Colorado, then what is it exactly that we share if there is nothing there but our brain states and we have different types of brain states?

At this point the materialists made a move that was crucial for subsequent philosophizing about the mind. They said: what token brain states have that makes them mental states is a certain type of function in the overall behavior of the organism. Not surprisingly, this doctrine was called “functionalism,” and when spelled out it developed into views like the following:17 to say that Jones believes that it is raining is to say that he has a certain event, state, or process going on in him that is caused by certain sorts of external stimuli—for example, he perceives that it is raining; and this phenomenon, in conjunction with certain other factors, such as his desire to stay dry, will cause a certain sort of behavior on his part, the behavior of carrying an umbrella. Mental states, in short, are defined as states that have certain sorts of functions, and the notion of function is explained in terms of causal relations to external stimuli, to other mental states, and to external behavior.

Mental states such as beliefs are not defined by any intrinsic features, rather they are defined by their causal relations, and these causal relations constitute their function.

Beliefs, for example, are caused by perceptions and together with desires they cause actions. Such causal relations are all that there is to having a belief.

another appeal of the functionalist account of mental states is that it seemed to assimilate the mental realm to a very familiar realm of human functional entities. Thus if we ask, What is a carburetor? What is a thermostat? What is a clock?—all of these questions are answered causally, by describing the causal functions performed by carburetors, thermostats, and clocks. None of these things are defined by their physical structure. A clock, for example, can be made out of gears and wheels, it can be made out of an hourglass with sand in it, it can be made out of quartz oscillators, it can be made out of any number of physical materials, but the defining feature of a clock is that it is any physical mechanism that enables us to tell the time. Analogous remarks could be made about carburetors and thermostats. Mental states are like carburetors, thermostats, and clocks. They are defined not by their physical structure and not by any Cartesian mental essence; rather, they are defined by their causal relations. A belief is just any entity that, standing in certain relationships to input stimuli and to other mental states, will cause external behavior.

The functionalists naturally wanted to know what was the nature of the inner mental brain states that enabled them to cause behavior. How did the mental states differ from other sorts of brain states? One answer was to say that this is not really a suitable question for philosophy at all; it should be left to psychologists and neurobiologists. We can treat the brain as just a “black box,” which produces behavior in response to stimuli, and we need not, as philosophers, worry about the mechanism inside the black box. This view was sometimes called “black-box functionalism.” But black-box functionalism is intellectually unsatisfying in that it does not answer our natural intellectual curiosity. We want to know, really, how does the system work?

The idea was based on a convergence of work in philosophy, cognitive psychology, linguistics, computer science, and artificial intelligence. It seemed that we knew the answer to the question that faced us: the way the system works is that the brain is a digital computer and what we call the “mind” is a digital computer program or set of programs. We had made the greatest breakthrough in the history of philosophy of mind: mental states are computational states of the brain. The brain is a computer and the mind is a program or set of programs. A principle that formed the foundation for any number of textbooks was this: the mind is to the brain as the program is to the hardware.18 This view is sometimes called “computer functionalism,” though I have also baptized it “Strong Artificial Intelligence” to distinguish it from Weak Artificial Intelligence, which aims to…

An algorithm is a method for solving a problem by going through a precise series of steps. The steps must be finite in number, and if carried out correctly, they guarantee a solution to the problem. For this reason algorithms are also called “effective procedures.” Good examples are the methods used to solve problems in arithmetic, such as addition and subtraction. If you follow the steps exactly, you will get the correct solution.

A Turing machine is a device that carries out calculations using only two types of symbols. These are usually thought of as zeros and ones, but any symbols will do. The idea of the Turing machine was invented by Alan Turing, the great British logician and mathematician. The striking feature of the Turing machine is its simplicity: it has an endless tape on which the symbols are written. It has a head that reads symbols on the tape. The Turing machine head will move to the left or to the right, it can erase a zero, it can print a one, it can erase a one, it can print a zero. It does all of these things in accordance with a program, which consists of a set of rules. The rules always have the same form; under condition C, perform act A: C A. For example, a rule might be of the form, if you are scanning a zero, replace it with a one and move one square to the left. A Turing machine is not a machine in the ordinary sense. You cannot go into a store and buy a Turing machine. It is an abstract mathematical concept.

Due originally to Alonzo Church (arrived at independently by Turing, so sometimes called the Church-Turing Thesis), this thesis states that any problem that has an algorithmic solution can be solved on a Turing machine. Or another way to say the same thing is that any algorithm at all can be carried out on a Turing machine. The idea of a machine that just uses binary symbols, zeros and ones, is sufficient to carry out any algorithm whatever. This is a very important thesis because it says in mathematical terms that any problem that is computable can be computed on a Turing machine. Any computable function is Turing computable.

Turing, in an important mathematical result known as Turing’s Theorem, proved that there is a Universal Turing machine that can simulate the behavior of any other Turing machine. More precisely, Turing proved that there is a Universal Turing machine, UTM, such that for any Turing machine carrying out a specific program, TP, UTM can carry out TP. What made these ideas so exciting was the following thought: Suppose the human brain is a Universal Turing machine? I cannot exaggerate the excitement that this idea generated, because it gave us at long last not just a solution to the philosophical problems that beset us, but it gave us a research program. We can study the mind, we can find out how the mind really works, by discovering which programs are implemented in the brain. An immensely appealing feature of this research program is that we do not actually have to know how the brain works as a physical system in order to do a complete and strict science of the mind.

We need a test that will tell us when a machine is genuinely behaving intelligently, and when it is not. This test was also invented by Alan Turing, and is called the Turing test. There are different versions of it, but the basic idea is this: we can side-step all the great debates about the other minds problem, about whether or not there really is any thinking going on in the machine, whether the machine is really intelligent, by simply asking ourselves, Can the machine perform in such a way that an expert cannot distinguish its performance from a human performance? If the machine responds to questions put to it in Chinese as well as a native Chinese speaker, so that other native Chinese speakers could not tell the difference between the machine and a native Chinese speaker, then we would have to say that the machine understood Chinese. The Turing test, as you will have noticed, expresses a kind of behaviorism. It says that the behavioral test is conclusive for the presence of mental states.

Any complex system can be described in different ways. Thus, for example, a car engine can be characterized in terms of its molecular structure, in terms of its gross physical shape, in terms of its component parts, etc. It is tempting to describe this variability of descriptive possibilities in terms of the metaphor of “levels,” and this terminology has become generally accepted. We think of the microlevel of molecules as a lower level of description than the level of gross physical structure or physical components, which are higher levels of description. Most of the interest of this distinction is that it applies in a dramatic fashion to computers. At a lower level of description your computer and mine might be quite different. Yours may have a different type of processor than mine, for example. But at a higher level of description they may be implementing exactly the same algorithm. They may be carrying out the same program.

Yet another important idea, already implicit in what I have said, is that big complex problems can be broken down into little simple problems, which can be broken down into even simpler problems, until we reach the level of ultimate simplicity. Doing multiplication with several digits, for example multiplying 28 x 71, may seem to us a complex operation, but the beauty of the idea of a Turing machine is that at bottom, all such problems break down into simple maneuvers with zeros and ones.

Again, the idea of recursive decomposition seemed to give us an important clue to understanding human intelligence. Complex intelligent human tasks are recursively decomposable into simple tasks, and that is how we are so intelligent.

The collection of ideas that I have just explained contains the tools necessary to articulate the single most influential and powerful theory of the mind in the last decades of the twentieth century. The brain is a digital computer, in all probability a Universal Turing machine. As such it carries out algorithms by implementing programs, and what we call the mind is a program or a set of such programs. To understand human cognitive capacities it is only necessary to discover the programs that human beings are actually implementing when they activate such cognitive capacities as perception, memory, etc. Because the mental level of description is a program level, we do not need to understand the details of how the brain works in order to understand human cognition. Indeed, because the level of description is at a higher level than neuronal structures, we are not forced to any type-type identity theory of the mind. Rather, mental states are multiply realizable in different sorts of physical structures, which just happen to be implemented in brains but could equally well have been implemented in an indefinite range of computer hardwares. Any hardware implementation will do for the human mind provided only that it is stable enough and rich enough to carry the programs.

And we now have a research project; indeed, it is the research project of cognitive science. We try to discover the programs that are implemented in the brain by designing programs for our commercial machines that will pass the Turing test, and then we ask the psychologists to perform experiments on humans to see if they are following the same program as the program on our computer. For example, in one famous experiment involving the memory of numbers, the reaction times of the subjects seemed to vary in the same way as the processing time of a computer. This seemed to a lot of cognitive scientists good evidence that the humans were using the algorithmic procedures of the computer.

Anomalous monism is a view put forward by Donald Davidson20 for which he advances the following argument: Step 1: There are causal relations between mental phenomena and physical phenomena. Step 2: Wherever there are events related as cause and effect they must fall under strict, deterministic causal laws. Step 3: But there are no such strict deterministic causal laws relating the mental and the physical. In Davidson’s terms, there are no psycho-physical laws. Therefore, Step 4: Conclusion. All so-called mental events are physical events. They have to be physical events to instantiate physical laws, and when we describe them as mental, we are just picking out a category of physical events that satisfy a certain mental vocabulary. They are mental under one description, but the same events are also physical under another description. The result, then, is a kind of materialism, a materialism that says that the subject matter of the psychological sciences will never be describable by the kinds of universal laws that we get in physics, not because they are a mysterious kind of spiritual or mental entity, but rather because the descriptions we use to pick them out, the mental descriptions, do not relate in a lawlike fashion to physical phenomena picked out under physical descriptions. The only argument that Davidson gives for this point is that mental phenomena, like beliefs and desires, are subject to constraints of rationality, and rationality has “no echo in physics.”

In this chapter I will present the most common arguments against materialism, concentrating on functionalism, because it is currently the most influential version of materialism. In general, these attacks have the same logical structure: the materialist account leaves out some essential feature of the mind such as consciousness or intentionality. In the jargon of philosophers, the materialist analysis fails to give sufficient conditions for mental phenomena, because it is possible to satisfy the materialist analysis and not have the appropriate mental phenomena.

Conscious experiences have a qualitative aspect. There is a qualitative feel to drinking beer, which is quite different from the qualitative feel of listening to Beethoven’s Ninth Symphony. Several philosophers have found it useful to introduce a technical term to describe this qualitative aspect of consciousness. The term for qualitative states is “qualia,” of which the singular is “quale.” Each conscious state is a quale, because there is a certain qualitative feel to each state.

One of the earliest well-known arguments against functionalist types of materialism was advanced in an article by Thomas Nagel called, “What It Is Like to Be a Bat?”1 According to Nagel, the really difficult part of the mind-body problem is the problem of consciousness. Suppose we had a fully satisfactory functionalist, materialist, neurobiological account of various mental states: beliefs, desires, hopes, fears, etc. All the same, such an account would not explain consciousness. Nagel illustrates this with the example of a bat. Bats have a different lifestyle from ours. They sleep all day long, hanging upside down from rafters, and then they fly around at night, navigating by detecting echoes from sonar they bounce off of solid objects. Now, says Nagel, someone might have a complete knowledge of a bat’s neurophysiology; he might have a complete knowledge of all the functional mechanisms that enable bats to live and navigate; but all the same, there would be something left out of this person’s knowledge: What is it like to be a bat? What does it feel like? And this is the essence of consciousness. For any conscious being, there is a what-it-is-like aspect to his existence. And this is left out of any objective account of consciousness because an objective account cannot explain the subjective character of consciousness.

A similar argument was advanced by the Australian philosopher, Frank Jackson.2 Jackson imagines a neuro-biologist, Mary, who knows all there is to know about color perception. She has a total and complete knowledge of the neurophysiology of our color-perceiving apparatus, and she also has a complete knowledge of the physics of light and of the color spectrum. But, says Jackson, let us imagine that she has been brought up entirely in a black and white environment. She has never seen anything colored, only black, white, and shades of gray. Now, says Jackson, it seems clear that there is something left out of her knowledge. What is left out, for example, is what the color red actually looks like. But, then, it seems that a functionalist or a materialist account of the mind would leave something out, because a person might have the complete knowledge of all there was to know on a functionalist or materialist account, without knowing what colors look like. And the problem with colors is only a special case of the problem of qualitative experiences generally. Any account of the mind that leaves out these qualitative experiences is inadequate.

Kripke’s argument appeals to the concept of a “rigid designator.” A rigid designator is defined as an expression that always refers to the same object in any possible state of affairs. Thus, the expression, “Benjamin Franklin,” is a rigid designator because in the usage that I am now invoking, it always refers to the same man. This is not to say, of course, that I cannot name my dog “Benjamin Franklin,” but, then, that is a different usage, a different meaning of the expression. On the standard meaning, “Benjamin Franklin” is a rigid designator. But the expression, “The inventor of daylight saving time,” though it also refers to Benjamin Franklin, is not a rigid designator because it is easy to imagine a world in which Benjamin Franklin was not the inventor of daylight saving time. It makes sense to say that someone else, other than the actual inventor, might have been the inventor of daylight saving time, but it makes no sense to say that someone else, other than Benjamin Franklin, might have been Benjamin Franklin. For these reasons, “Benjamin Franklin” is a rigid designator, but “the inventor of daylight saving time” is nonrigid.

An argument explicitly directed against Strong AI was put forth by the present author.5 The strategy of the argument is to appeal to one’s first person experiences in testing any theory of the mind. If Strong AI were true, then anybody should be able to acquire any cognitive capacity just by implementing the computer program simulating that cognitive capacity. Let us try this with Chinese. I do not, as a matter of fact, understand any Chinese at all. I cannot even tell Chinese writing from Japanese writing. But, we imagine that I am locked in a room with boxes full of Chinese symbols, and I have a rule book, in effect, a computer program, that enables me to answer questions put to me in Chinese. I receive symbols that, unknown to me, are questions; I look up in the rule book what I am supposed to do; I pick up symbols from the boxes, manipulate them according to the rules in the program, and hand out the required symbols, which are interpreted as answers. We can suppose that I pass the Turing test for understanding Chinese, but, all the same, I do not understand a word of Chinese. And if I do not understand Chinese on the basis of implementing the right computer program, then neither does any other computer just on the basis of implementing the program, because no computer has anything that I do not have. You can see the difference between computation and real understanding if you imagine what it is like for me also to answer questions in English. Imagine that in the same room I am given questions in English, which I then answer. From the outside my answers to the English and the Chinese questions are equally good. I pass the Turing test for both. But from the inside, there is a tremendous difference. What is the difference exactly? In English, I understand what the words mean, in Chinese I understand nothing. In Chinese, I am just a computer.

as far as human cognition is concerned, such achievements are simply irrelevant. And they are irrelevant for a deep reason: the computer operates by manipulating symbols. Its processes are defined purely syntactically, whereas the human mind has more than just uninterpreted symbols, it attaches meanings to the symbols.

When I add two plus two to get four, that computation is not observer relative. I am doing that regardless of what anybody thinks. But when I punch: ”2+2 =” on my pocket calculator and it prints out “4” it knows nothing of computation, arithmetic, or symbols, because it knows nothing about anything. Intrinsically it is a complex electronic circuit that we use to compute with. The electrical state transitions are intrinsic to the machine, but the computation is in the eye of the beholder. What goes for the calculator goes for any commercial computer. The sense in which computation is in the machine is the sense in which information is in a book. It is there alright, but it is observer relative and not intrinsic. For this reason you could not discover that the brain is a digital computer, because computation is not discovered in nature, it is assigned to it. So the question, Is the brain a digital computer? is ill defined. If it asks, Is the brain intrinsically a digital computer? the answer is that nothing is intrinsically a digital computer except for conscious agents thinking through computations.

The distinction between syntax and semantics is so important for the rest of the argument of this book that I want to say a little more about it here. In order that there can be human linguistic communication at all, there has to be a language. A language consists of symbols, typically words, combined into sentences. These elements, symbols, words, sentences, are all syntactical. But language only works if these elements are meaningful—if they carry meaning. But what is meaning? There are many different accounts of meaning in the philosophical, linguistic, and psychological literature. I have definite opinions about which are right and which are wrong, but for the purposes of this argument those disputes do not matter. Any sane account of meaning has to recognize the distinction between the symbols, construed as purely abstract syntactical entities, and the meanings attached to those symbols. The symbols have to be distinguished from their meanings. For example, if I write down a sentence in German, “Es regnet,” you will see words on the page and thus see the syntactical objects, but if you do not know German, you will be aware only of the syntax, not of the semantics. You will be in the situation that I am in in the Chinese Room, where I am aware of the syntax of the computational system, but I do not know what any of it means.

Forget about consciousness, which is scientifically irrelevant anyway. What matters about the mind is its capacity for information processing, and the modern computer at long last gives us the right model for understanding the information processing capacities of the mind. This conception in modern materialism that consciousness could be set on one side, while we concentrated on intentionality, is why there were so many more attacks on the Chinese Room than on the other arguments. It threatened the very citadel of the functionalist-computationalist account, which is the idea that if you had the right input-output relations, and if you had the right program mediating those relations, then you would have all there is to intentionality. The Chinese Room Argument shows that there are two things going on in the human being, one is the actual symbols that the human is aware of when he or she thinks, and second, there is the meaning, or interpretation, or sense that attaches to those symbols.

We end this chapter in a depressing intellectual state: neither dualism nor materialism is acceptable and yet they are presented to us as the only possibilities. Furthermore we know independently that both what dualism is trying to say and what materialism is trying to say are true. Materialism is trying to say that the world consists entirely of physical particles in fields of force. Dualism is trying to say that there are irreducible and ineliminable mental features to the world, consciousness and intentionality, in particular. But if both views are true, there must be a way of stating them that renders them consistent.

We ended the last chapter with an apparent contradiction of the sort that is typical in philosophy. On the one hand we accept a view that seems overwhelmingly convincing—the universe is material—but that seems inconsistent with another view that we cannot give up—minds exist. This pattern occurs over and over in philosophy. We will see in chapter 7 that the free-will problem exhibits the same sort of conflict or contradiction: we think all events must be causally determined, but we experience freedom. In other branches of philosophy, similar inconsistencies arise. In ethics we feel there must be an objective moral truth but at the same time we feel there cannot be that kind of objectivity in morals. Some people find these contradictions in philosophy exasperating. Others, like me, find them fun and challenging.

My method in philosophy is to try to forget about the history of a problem and the traditional ways of thinking about it and just try to state the facts as far as we know them.

Suppose an animal gets a shortage of water in its system. The shortage of water will cause “saline imbalances” in the system, because the ratio of salt to water is excessive in favor of salt. This triggers certain activities in the kidneys. The kidneys secrete rennin, and the rennin synthesizes a substance called angiotensin 2. This substance gets inside the hypothalamus and affects the rate of neuron firings. As far as we know the differential rates of neuron firings cause the animal to feel thirsty. Now, of course, we do not know all of the details and no doubt as we come to understand more, this brief sketch I have given will seem quaint. But that is the sort of explanation of how the existence of conscious feelings of thirst fits into our overall world-view. All forms of consciousness are caused by the behavior of neurons and are realized in the brain system, which is itself composed of neurons. What goes for thirst goes for all forms of our conscious life whatever, from wanting to throw up to wondering how to translate the poems of Stéphane Mallarmé into colloquial English. All conscious states are caused by lower-level neuronal processes in the brain. We have conscious thoughts and feelings; they are caused by neurobiological processes in the brain; and they exist as biological features of the brain system. I believe that this brief account provides the germ of a solution to the “mind-body problem”: I am suspicious of isms, but it is sometimes helpful to have a name, just to distinguish clearly between one view and another. I call my view “biological naturalism,” because it provides a naturalistic solution to the traditional “mind-body problem,” one that emphasizes the biological character of mental states, and avoids both materialism and dualism. I will state biological naturalism about consciousness as a set of four theses: 1. Conscious states, with their subjective, first-person ontology, are real phenomena in the real world. We cannot do an eliminative reduction of consciousness, showing that it is just an illusion. Nor can we reduce consciousness to its neurobiological basis, because such a third-person reduction would leave out the first-person ontology of consciousness. 2. Conscious states are entirely caused by lower level neurobiological processes in the brain. Conscious states are thus causally reducible to neurobiological processes. They have absolutely no life of their own, independent of the neurobiology. Causally speaking, they are not something “over and above” neurobiological processes. 3. Conscious states are realized in the brain as features of the brain system, and thus exist at a level higher than that of neurons and synapses. Individual neurons are not conscious, but portions of the brain system composed of neurons are conscious. 4. Because conscious states are real features of the real world, they function causally. My conscious thirst causes me to drink water for example. I will explain in detail how this works in…

The worst mistake is to suppose that the common-sense distinction between mental states naïvely construed and physical states naïvely construed is an expression of some deep metaphysical distinction. On the view that I am presenting, it is not. Consciousness is a system-level, biological feature in much the same way that digestion, or growth, or the secretion of bile are system level, biological features. As such, consciousness is a feature of the brain and thus a part of the physical world. The tradition that I am militating against says that because mental states are intrinsically mental, they cannot be in that very respect, physical.

This is one of the most important messages of this book. Once you revise the traditional categories to fit the facts, there is no problem in recognizing that the mental qua mental is physical qua physical. You have to revise the traditional Cartesian definitions of both “mental” and “physical,” but those definitions were inadequate to the facts in any case.

So consciousness differs from other phenomena such as liquidity and solidity that have surface features, in that we are reluctant to carve off the surface feature and redefine the notion in terms of the causes of the surface feature, because the point of the concept is to identify the surface features. There are lots of concepts where the surface features of the phenomena are more interesting than the microstructure. Consider mud or Beethoven’s Ninth Symphony. Mud behavior is molecular behavior but that it not the interesting thing about mud, so few people are anxious to insist: “Mud can be reduced to molecular behavior,” though they could if they really wanted to. Similarly with Beethoven. Performances of the Ninth can be reduced to wave motions in the air, but that is not what is interesting to us about the performance. The music critic who writes, “All I could hear were wave motions,” has missed the point of the performance. Analogously you could do a reduction of consciousness and intentionality, but you would still need a vocabulary to talk about the surface features. Consciousness and intentionality are unique only in that they have a first-person ontology.

there is an asymmetry between colors on the one hand and pains and consciousness on the other, because we would lose the point of having the concepts of consciousness if we carved off the first-person ontology and redefined the words in third-person terms. In that sense the irreducibility of consciousness does not reveal a deep metaphysical asymmetry between, for example, the way color experiences relate to their causes and the way pain experiences relate to their causes, but rather an asymmetry in our definitional practices. For the definition of “pain” we care more about how pains feel to us than we do for the definition of “color.”

But why couldn’t we show that consciousness was an illusion like sunsets and thus do an eliminative reduction? Eliminative reductions rest on the distinction between appearance and reality. But we cannot show that the very existence of consciousness is an illusion like sunsets, because where consciousness is concerned the appearance is the reality. The sun appears to set over Mt. Tamalpais though it does not really do so. But if it consciously seems to me that I am conscious, then I am conscious. I can make all sorts of mistakes about the contents of my conscious states, but not in that way about their very existence.

Materialism tries to say truly that the universe is entirely made up of physical particles that exist in fields of force and are often organized into systems. But it ends up saying falsely that there are no ontologically irreducible mental phenomena. Dualism tries to say truly that there are irreducible mental phenomena. But it ends up saying falsely that these are something apart from the ordinary physical world we all live in, that they are something over and above their physical substrate. The challenge is to state the true part of each view and deny the false part. If you stick with the traditional vocabulary it seems impossible to do that, because you end up saying that the irreducible (subjective, qualitative) mental is just an ordinary part of the physical world, and that sounds self-contradictory. So in the end I have tried to challenge the traditional vocabulary.

On the dualist’s conception, consciousness is definitely something over and above its material substrate. Indeed the dualist supposes that the irreducibility of consciousness already implies that consciousness is something over and above its neurobiological base. I deny that implication. This point is so crucial for the entire argument of this book that I am going to spell it out in some detail. The fact that the causal powers of consciousness and the causal powers of its neuronal base are exactly the same shows that we are not talking about two independent things, consciousness and neuronal processes. If two things in the real empirical world have an independent existence they must have different causal powers. But the causal powers of consciousness are exactly the same as those of the neuronal substrate. This situation is exactly like the causal powers of solid objects and the causal powers of their molecular constituents. We are not talking about two different entities but about the same system at different levels. Consciousness differs from solidity, liquidity, etc., in that the causal reduction does not lead to an ontological reduction. This, as we have seen, is so for an obvious, and indeed trivial, reason. Consciousness has a first-person ontology; neuronal processes have a third-person ontology. For that reason you cannot ontologically reduce the former to the latter. Consciousness is thus an aspect of the brain, the aspect that consists of ontologically subjective experiences. But there are not two different metaphysical realms in your skull, one “physical” and one “mental.” Rather, there are just processes going on in your brain and some of them are conscious experiences.

Once again it seems to me the illusion of dualism is generated by misunderstanding a very real distinction. There really is a distinction between those irreducible features of the world that have a first-person or subjective ontology and those that do not. But it is a deep mistake to suppose that that real distinction is the same as the old-time distinction between the mental and the physical, between res cogitans and res extensa, or that the subjective phenomena are something over and above the systems in which they are realized.

Think of it this way: roughly speaking, consciousness is to neurons as the solidity of the piston is to the metal molecules. Both consciousness and solidity function causally. But neither is “over and above” the systems of which they are a part.

The refutation of dualism is harder. Let us define dualism as the view that there are two distinct metaphysical ontological realms in the universe, one mental the other physical. This is harder to refute, because whereas materialism postulated the nonexistence of something we know to exist, this view postulates the existence of something, and to refute it formally you would have to prove a universal negative. Rather than give a formal “refutation,” I will give what I take to be conclusive arguments against dualism. 1. No one has ever succeeded in giving an intelligible account of the relationships between these two realms. 2. The postulation is unnecessary. It is possible to account for all of the first-person facts and all the third-person facts without the postulation of separate realms. 3. The postulation creates intolerable difficulties. It becomes impossible on this view to explain how mental states and events can cause physical states and events. In short, it is impossible to avoid epiphenomenalism. Notice that these arguments still leave dualism as a logical possibility. It is a logical possibility, though I think extremely unlikely, that when our bodies are destroyed, our souls will go marching on. I have not tried to show that this is an impossibility (indeed, I wish it were true), but rather that it is inconsistent with just about everything else we know about how the universe works and therefore it is irrational to believe in it.

The fact that conscious states are ontologically subjective, in the sense that they exist only as experienced by a human or animal subject, does not imply that there cannot be a scientifically objective study of conscious states. “Objective” and “subjective” are systematically ambiguous between an ontological and an epistemic sense. In the epistemic sense, there is a distinction between those statements that can be ascertained as true or false independently of the feelings and attitudes of the speakers or hearers and those statements whose truth or falsity depends on those feelings and attitudes. Thus the statement “Jones is six feet tall” is epistemically objective because its truth or falsity has nothing to do with the feelings and attitudes of the speaker and hearer. But the statement “Jones is a nicer person than Smith” is epistemically subjective because its truth or falsity cannot be settled independently of the feelings and attitudes of the participants in the discussion. In addition to this epistemic sense, there is a distinction between two modes of existence.

the whole science of neurology requires that we try to seek an epistemically objective scientific account of pains, anxieties, and other afflictions that patients suffer from in order that we can treat these with medical techniques. Whenever I hear philosophers and neurobiologists say that science cannot deal with subjective experiences I always want to show them textbooks in neurology where the scientists and doctors who write and use the books have no choice but to try to give a scientific account of people’s subjective feelings, because they are trying to help actual patients who are suffering.

I used to think that these three features, qualitativeness, subjectivity, and unity, could be described as distinct features of consciousness. It now seems to me that that is a mistake; they are all aspects of the same phenomenon. Consciousness is by its very essence qualitative, subjective, and unified. There is no way that a state could be qualitative, in the sense that I have introduced, without it also being subjective in the sense that I have explained. But there is no way that the state could be both qualitative and subjective, without having the kind of unity that I have been describing.

One of the ways to study consciousness is to study the pathological or degenerate forms of consciousness, and this is a method that I will use several times in this book. The split-brain patients suffered from terrible forms of epilepsy that could not be treated by the normal methods. In desperation, the doctors cut the corpus callosum, the body of tissue that connects the two brain hemispheres. This did, in fact, cure many of the patients of epilepsy, but it had some other interesting effects. Most strikingly, it caused the patient to behave in certain circumstances as if he had two independent centers of consciousness. In a typical experiment the following occurs: the patient is shown a spoon, but the spoon is put in a portion of his left visual field so that the visual stimulus only goes to the right side of his brain. Language is on the left side of his brain. He is then asked, “What do you see?” Since he has no visual perception of the spoon on the left side of the brain where he has language; and since, because of the severed corpus callosum, there is only very imperfect communication between the two hemispheres, the patient in such a case says, “I do not see anything.” However, he then reaches out with his left hand, which is controlled by his right hemisphere, where the visual experience of the spoon does occur, and grabs the spoon. There is a large number of experiments of this kind conducted by Roger Sperry and Michael Gazzaniga.2 Does the patient have one or two centers of consciousness? At present, we just do not know for sure. But, at least, we have to consider the possibility that there are, in fact, two conscious fields inside one brain, one corresponding to each hemisphere and that in the normal case the two fields of consciousness coalesce into a single unified conscious field.

This feature, whereby many of my experiences seem to refer to things beyond themselves, is the feature that philosophers have come to label “intentionality.” Not all consciousness is intentional, and not all intentionality is conscious, but there is a very serious and important overlap between consciousness and intentionality, and later we will see that there are, in fact, logical connections between the two: mental states that are in fact unconscious have to be the kind of thing that could in principle become conscious. For a number of reasons, ranging from brain damage to psychological repression, they may be in fact inaccessible to consciousness, but they have to be the sort of thing that could be part of a conscious mental state. An example of a conscious state that is not intentional is the sense of anxiety that one sometimes gets when one is not anxious about anything in particular but just has a feeling of anxiousness.

Our conscious experiences do not just come to us as a disorganized mess; rather they typically come to us with well-defined, and sometimes even precise, structures. We do not, for example, in normal vision see undifferentiated blurs and fragments; rather, we see tables, chairs, people, cars, etc., even though only fragments of those objects are reflecting photons at the retina, and the retinal image is in various ways distorted. The Gestalt psychologists investigated these structures and found certain interesting facts. One is, the brain has a capacity to take degenerate stimuli and organize them into coherent wholes. Furthermore, it is able to take a constant stimulus and treat it now as one perception, now as another. So in the famous “duck-rabbit” example there is a constant perceptual input but I perceive it now as a duck, now as a rabbit. In these drawings, the left-hand figure does not actually physically resemble a human face, but nonetheless, you will perceive it as a face because your brain organizes the degernate stimulus into a coherent whole. The right-hand figure is the famous duck-rabbit, which can be seen either as a duck or as a rabbit. Furthermore, the Gestalt structure is not only a matter of organizing our perceptions into coherent wholes, but within the entire conscious field, we make a distinction between the figures that we are perceiving and the ground on which they are perceived. So, for example, I see the pen against the background of the book, the book against the background of the desk, the desk against the background of the floor, and the floor against the rest of the room, until I reach the horizon of my entire perceptual field. There are thus two aspects, at least, to the Gestalt structure of consciousness. First, the capacity that the brain has to organize perceptions into coherent wholes, and second, the capacity that the brain has to discriminate figures from backgrounds.

Mysterians think that consciousness is a mystery that cannot be solved by our existing scientific methods; and some mysterians think we will never be able to understand how consciousness could be explained by brain processes. Thomas Nagel5 thinks it might be possible one day to understand how brain causes consciousness but it would require a total revolution in our way of thinking about reality and in our conception of scientific explanation, because given our present apparatus we cannot conceive how subjective, qualitative inner experiences could arise from third-person neuronal phenomena. Colin McGinn,6 an extreme mysterian, thinks it is impossible in principle that human beings should ever come to be able to understand how the brain causes consciousness.

nature is radically contingent. Many of the most important explanatory principles in science are by no means intuitive or obvious. Think of the Schroedinger equation or Planck’s constant or for that matter, Einstein’s famous e=mc2. In each case, this is just how nature turned out. It did not have to turn out that way, but that is in fact how it did turn out. I am with Hume in thinking that the conviction that nature must necessarily be the way it is, is an illusion. So, for example, even when the billiard ball strikes the other billiard ball, it is just a fact of nature that the second will move. But it could equally well be a fact of nature that they both move backward or that the first would swallow the second. It is just that nature turned out one way and not another way. Nature is full of surprises. We should never forget, for example, that liquid helium 3 placed in a container will climb up its side.

Pan-psychism is the view that consciousness is everywhere. This view is seldom stated explicitly, but it is implicit in several authors particularly among the mysterians who think that if we are going to explain consciousness in terms of microprocesses, then, somehow or other, some form of consciousness must already be present in the microprocesses. At one time Thomas Nagel flirted with this view, and David Chalmers8 explores it and supports it, though he does not explicitly endorse it. On this view, everything is conscious to some degree. In giving an example of the ubiquity of consciousness, Chalmers eloquently describes what it might be like to be a conscious thermostat.

our present era is remarkable in that there is a large number of very able neurobiologists attempting to figure out exactly how brain processes cause conscious states. Ideally, such a research project proceeds in the three stages I mentioned earlier. First, find the neuronal correlate of consciousness, called the NCC; second, test to see if the correlation is causal; third, get a theory. I think that we can divide this research for the purpose of our analysis into two different camps that I call respectively the “building-block approach” and the “unified-field approach.” On the building-block approach, we treat the entire conscious field as made up of more-or-less independent conscious units that I call “building blocks.” The experience of red, the taste of the beer, the sound of middle C, would be examples of the sorts of building blocks I have in mind. The idea of the building-block approach is this: if we could figure out exactly how the brain causes even one building block, say the perception of red, then we might use that knowledge to crack the whole problem of consciousness.

The second approach to the problem of consciousness, the unified-field approach, begins by taking seriously the feature of qualitative subjective unity that I mentioned earlier. For this approach, the paradigm of consciousness, the initial target of the investigation, is not such things as the experience of the color red, but rather the whole conscious field of qualitative, unified subjectivity. For this approach the basic question is not, How does the brain produce this specific building block in the conscious field? but how does it produce the whole conscious field in the first place? What is the difference between the conscious brain and the unconscious brain, and how does that difference causally explain consciousness?

To make matters even worse, it seems that I can sometimes think about objects that do not even exist. When I was a small child I believed that Santa Claus comes on Christmas Eve. Was my belief about Santa Claus? It certainly seems so, but how is that possible, since Santa Claus does not even exist? Notice that these are questions that only a philosopher would ask. Philosophy begins with a sense of mystery and wonder at what any sane person regards as too obvious to worry about.

There are three problems about intentionality we need to address. First, how is intentionality possible at all; second, given that intentional states are possible, how is their content determined; and third, how does the whole system of intentionality work? Most of the philosophical literature is about the first two questions.

Readers familiar with cognitive science will recognize that when we talk about intentionality we are discussing what in cognitive science is known as “information.” I prefer “intentionality” because “information” is systematically ambiguous between a genuinely observer-independent mental sense (for example, by looking out the window now I have information about the weather) and a nonmental observer-relative sense (for example, the rings in the tree stump contain information about the age of the tree). This ambiguity can also arise for “intentionality,” but it is easier to avoid and confusion is less likely.

I. HOW IS INTENTIONALITY POSSIBLE AT ALL? This problem is supposed to be as difficult as the problem of consciousness, so the sorts of solutions that are supposed to solve it are much like the solutions proposed for the problem of consciousness. The dualistic solution is to say that as there are two different realms, the mental and the physical, so the mental realm has its own sorts of powers not possessed by the physical realm. The physical realm is incapable of referring, but the mental realm is essentially capable of thinking, and thinking involves reference. I hope it is obvious that this dualistic solution is no solution at all. To explain the mystery of intentionality it appeals to the mystery of the mental in general. I think that the most common contemporary philosophical solution to the problem of intentionality is some form of functionalism. The idea is that intentionality is to be analyzed entirely in terms of causal relations. These causal relations exist between the environment and the agent and between various events going on inside the agent. On this view there is nothing mysterious about intentionality. It is just a form of causation. The only special feature is that intentional relations exist between the agent’s cerebral innards and the external world. And, by this time, I do not need to tell the reader that the most influential version of functionalism is computer functionalism, or Strong Artificial Intelligence. Finally, there is the eliminativist view of intentionality: there really are no intentional states. The belief that there are such things is just a residue of a primitive folk psychology, one that a mature science of the brain will enable us to overcome. A variant of the eliminativist view is what we might…

We are speaking, as we did about consciousness, of a certain set of biological capacities of the mind. And it is best to start with the biological capacities that are primitive—for instance, hunger, thirst, the sex drive, perception, and intentional action. In the last chapter I described some of the neurobiological details about how brain processes cause conscious feelings of thirst. But in explaining how brain processes can cause feelings of thirst, we have already explained how brain processes can cause forms of intentionality, because thirst is an intentional phenomenon. To be thirsty is to have a desire to drink. When the angiotensin 2 gets inside the hypothalamus and triggers the neuronal activity that eventually results in the feeling of thirst it has eo ipso resulted in an intentional feeling. The basic forms of consciousness and intentionality are caused by the behavior of neurons and are realized in the brain system, that is itself composed of neurons. What goes for thirst goes for hunger and fear and perception and desire and all the rest. Once we demystify the problem of intentionality by removing it from the abstract, spiritual level down to the concrete level of real animal biology, I do not believe that any unsolvable mystery remains about how it is possible for animals to have intentional states. If you start with such simple and obvious cases as hunger and thirst, intentionality is not at all difficult to explain. Of course, beliefs, desires, and sophisticated forms of thought processes are more complex and more removed from the immediate stimulation of the brain by the impact of the environment than are perceptions or feelings of hunger and thirst. But even they are caused by brain processes and realized in the brain system.

At this point, it seems to me the best thing I can do is describe the formal structure of intentional states, because we will not get a grasp on how intentionality functions, until we see the structural features of intentional states, such as beliefs and desires, hopes and fears, perceptions, memories, and intentions.

Because intentional states are capable of referring to objects and states of affairs in the world beyond themselves, they must have some sort of content that determines this reference, and indeed we need to distinguish the content of the state from the type of state that it is. Thus I can believe that it will rain, hope that it will rain, fear that it will rain, or desire that it will rain. In each case there is the same content, that it will rain, but that content relates to the world in different psychological modes: belief, fear, hope, desire, etc. This distinction, by the way, exactly parallels the same distinction in language. Just as I can order you to leave the room, so I can predict that you will leave the room, and I can ask whether you will leave the room. In each case we have the same content, that you will leave the room, but it is presented in different sorts of speech acts. A good way to think of this is to think of the state as consisting in a psychological mode, such as belief or desire, with a propositional content, such as the proposition that it is raining. We can represent this as S(p), where the S stand for the mode or type of state and the p for the propositional content. Such states are often called “propositional attitudes.” Not all intentional states have an entire proposition as their content. One might just admire Eisenhower or love Marilyn, and in such cases the intentional state just refers to an object. Such states can be represented as S(n), where the n names or refers to an object. Notice that intentional representations are always under certain aspects and not others. For example, I might intentionally represent an object as the Evening Star and not as the Morning Star even though one and the same object is both. The aspect “celestial body that shines near the horizon in the evening” is not the same aspect as “celestial body that shines near the horizon in the morning.” Intentional states always have aspectual shapes, because all representation is under aspects. This is an important point, because any theory of intentionality must account for aspectual shape, and some materialist theories are unable to do so. I mentioned in chapter 3 that functionalism was unable to distinguish between the desire for water and the desire for H2O and this is because the causal relations on which functionalism relies to analyze intentionality do not have the aspectual shapes characteristic of genuine intentionality.

Whenever we have an intentional state that has a non-null direction of fit, the fit will either be achieved or not: the belief will be true, the desire will be fulfilled, the intention will be carried out or not, as the case might be. In such cases, we can say that the belief, desire, or intention is satisfied. What stands to the belief’s being true is what stands to the desire’s being fulfilled, is what stands to the intention’s being carried out. I propose to describe this phenomenon by saying that every intentional state that has a non-null direction of fit has conditions of satisfaction. We can think of mental states as representations of their conditions of satisfaction. Indeed, I will argue later on that the key to understanding intentionality is conditions of satisfaction,

The most biologically basic intentional phenomena, including perceptual experiences, intentions to do something, and memories, have a peculiar logical feature in their conditions of satisfaction. It is part of the conditions of satisfaction of, for example, my memory that I went on a picnic yesterday, that if I really remember the event, then the event itself must cause my memory of it. If we spell out the conditions of satisfaction of the memory, they are not just that the event occurred, but also that its occurrence caused the very memory that has the occurrence of the event as the rest of its conditions of satisfaction. We can describe this by saying that memories, intentions, and perceptual experiences are all causally self-referential. What this means is that the content of the state itself refers to the state in making a causal requirement. The conditions of satisfaction of the memory itself require that the memory be caused by the event remembered. The conditions of satisfaction of the intention require that the performance of the action represented in the content of the intention requires that that very intention should cause that performance. And so on through other cases. In this respect, intentions, memories, and perceptual experiences are different from beliefs and desires. We can spell out the difference as follows. If I believe that I went on a picnic yesterday, then the formal structure of my intentional state looks like this:   Believe (I went on a picnic yesterday). But if I remember that I went on a picnic yesterday then the formal structure of my intentional state looks like this: Remember (I went on a picnic yesterday, and my going on a picnic caused this memory).

Intentional states do not in general come in isolated units. If I believe, for example, that it is raining, I cannot just have that belief in isolation. I must believe, for example, that rain consists of drops of water, that these fall out of the sky, that they generally go down and not up, that they make the ground wet, that they come out of clouds in the sky, and so on more or less indefinitely. Of course, someone might have the belief that it is raining and lack some of these other beliefs, but in general it seems that the belief that it is raining is only the belief that it is because of its position in a “network” of beliefs and other intentional states. And we can think of the totality of one’s intentional states as forming an elaborate interacting network. We can even say that any intentional state only functions, that is it only determines its conditions of satisfaction, relative to the network of which it is a part. If I believe I own a car, I must also believe that cars are modes of transportation, that they are used on streets and highways, that they move about, that people can get in and out of cars, that cars are a kind of property that can be bought and sold, and so on. If you follow out the threads in the network, you eventually reach a set of abilities, ways of coping with the world, dispositions, and capacities generally that I collectively call the “Background.” For example, if I form the intention to go skiing I can do so only if I take for granted that I have the ability to ski, but the ability to ski is not itself an additional intention, belief, or desire. I hold the controversial thesis that intentional states in general require a background of nonintentional capacities in order to function all.

I have given a very brief sketch of the formal structure of intentionality. We can summarize it as follows. For any intentional state, there is a distinction between the type of state it is, and its content. Where the content is a whole proposition, it will represent states of affairs in the world and it will do this with one of the three directions of fit, mind-to-world, world-to-mind, or null. Intentional states that have a non-null direction of fit are thus representations of their conditions of satisfaction. And given the network of intentionality, even those states that have the null direction of fit, and even those that do not have a whole propositional content, are still largely constituted by states that do have a non-null direction of fit. Thus if I am sorry that I stepped on your foot, I must believe that I did so and wish I had not done so. And if I admire Jimmy Carter I must have a set of beliefs and desires about Jimmy Carter. In general, intentionality is representation of conditions of satisfaction . The most biologically basic intentional states, those that relate animals directly to the environment, have a causally self-referential component in their conditions of satisfaction. Any intentional state can function, that is, it can determine conditions of satisfaction, only because of its position in a network of intentional states and against the background of pre-intentional capacities.

The formal structure of the intentionality that I have described is no trivial matter. This is in fact the structure of our conscious life. Indeed, it is the structure of our mental life, both conscious and unconscious. When we come to understand a social situation we are in, when we make up our minds to engage in some course of action, when we perceive the heavens on a starry night, when we suddenly have recollections of our childhood while eating a madeleine—all of these are manifestations of the formal structure that I have been describing. In order to understand our lives, we have to understand the structure of intentionality. It is important to emphasize that none of this…

Intentionality-with-a-t, as we have seen, is that property of the mind by which it is directed at or about or of objects and states of affairs in the world independent of itself. Intensionality-with-an-s is opposed to extensionality. It is a property of certain sentences, statements, and other linguistic entities by which they fail to meet certain tests for extensionality. The connection between the two is that many sentences about intentional-with-a-t states are intensional-with-an-s sentences. There are several such tests for extensionality, but the two most famous are the substitution test (sometimes called Leibnitz’s Law) and the test of existential inference. Let us consider each of these in order. The substitution test…

Formally we can put this as follows: 1. [(a=b) & Fa]Fb. If a is identical with b and a has property F, then b has property F. Thus from 2. Caesar crossed the Rubicon. and 3. Caesar is identical with Mark Anthony’s best friend. we can infer 4. Mark Anthony’s best friend crossed the Rubicon. For this reason, the occurrence of “Caesar” in 2 is said to be extensional with respect to substitutability. But there are sentences in which you cannot make the substitution. Thus from 5. Brutus believes that Caesar crossed the Rubicon. and the identity statement 3, we cannot validly infer 6. Brutus believes that Mark Anthony’s best friend crossed the Rubicon, because Brutus might not believe that Caesar is Mark Anthony’s best friend. Such a sentence is said to be intensional with respect to the occurrence of Caesar. It fails the test of substitutability. The principle of existential inference says that whenever a has the property F, you can validly infer that there exists an object that has the property F. 7. Fa (x)(Fx) Thus from 8. John lives in Kansas City. we can validly infer 9. There is some x such that John lives in x. But there are sentences of this form where we cannot validly make the…

The important thing to remember about the distinction between intentionality-with-a-t and intensionality-with-an-s is that there is nothing inherently intensional about intentionality. A statement to the effect that Brutus believes that Caesar crossed the Rubicon is indeed an intensional-with-an-s statement. But the belief itself, Brutus’s actual belief, does not thereby become intensional-with-an-s. The belief itself is as extensional as it can get. It will be true only if both Caesar and the Rubicon exist, (existential inference) and anything identical with Caesar crossed anything identical with the Rubicon (substitutability).

The view that I have been tacitly assuming throughout this book is a form of internalism. According to internalism, so construed, our intentional contents are entirely a matter of what is inside our heads. Of course they refer to objects and states of affairs in the world. That is what intentionality is for—to relate us to the world by representing its various features. The content that enables an intentional state to refer to one object rather than another is entirely between the ears of the referring subject. Internalism, so construed, has in recent decades been challenged by a series of arguments for the view that mental contents themselves are not in the head, or at least not entirely in the head, but in large part reside in relations between what is going on in the head and the rest of the world. It is important to see that this externalist theory is not merely claiming that our inner mental contents are often caused by external events (both sides agree on that) but rather that the contents themselves are not truly inner but are, at best, a mixture of the inner and outer. If that sounds vague, I am afraid it is, because externalism is a rather vaguely stated thesis.

You might think that “water” could be defined as a clear, colorless, tasteless liquid found in lakes and streams and coming out of the sky in the form of rain. But, says Hilary Putnam, that does not give the meaning of “water.” To see this, imagine a galaxy just like ours, with a planet in it just like our planet, that we will call Twin Earth. On Twin Earth everything is exactly the same as it is on Earth, molecule for molecule, with one exception. What we on Earth call “water” is made of H2O; what people on Twin Earth call “water” is not H2O but has a very long chemical formula that we can abbreviate as “XYZ.” Now, in 1750, before anybody knew anything about chemical composition, what was in the heads of the Twin Earth people when they used the word “water” was exactly the same as what was in the heads of the Earth people when they use the same word. But all the same, though the contents of the heads were the same, the meanings were different. Meanings cannot be in the head, because the same things are in their heads as are in our heads, but the meanings are different. “Water” on Earth refers to one kind of stuff; “water” on Twin Earth refers to another kind of stuff. The meaning on both Earth and Twin Earth, says Putnam, is determined by causal relations in which speakers stand to indexically presented substances. “Water” on Earth means whatever has the same structure as this indexically presented stuff. Ditto for Twin Earth. But since the stuffs are different, H2O in one case, XYZ in the other, the meanings are different. Meanings, concludes Putnam, “just ain’t in the head.”4 What goes for meaning goes for mental content generally. Beliefs employing the expression “water” are different for the people on Twin Earth than for the people on Earth. But if so, it turns out that beliefs cannot be entirely in the head. What is in the head is exactly the same in the two cases, though the beliefs are different.

What are we to make of these arguments? I admire the philosophical acumen of their authors, but I think both arguments are fallacious. The basic idea of internalism is that the mind—and by “mind” here we mean what is inside the head—sets conditions that an object must meet in order to be referred to by an expression or other form of thought content. In a classic example, the expression “the Morning Star” sets a condition such that if an object satisfies that condition, the expression can be used literally to refer to the object. Nothing in Putnam’s account challenges this conception. For the traditional idea that a checklist of features is associated with each word—for example, with the word “water” are associated such features as clear, colorless liquid, etc.—Putnam substitutes an indexical definition: “Water is anything identical in structure with what we are now seeing.” On our account of the causal self-referentiality of perceptual intentionality, that amounts to saying that water is whatever is identical in structure with the substance causing this very visual experience. But that definition sets a condition that is entirely represented in the contents of the mind.

We have already seen that an intentional state sets conditions of satisfaction. So for example, if I have the belief that Socrates drinks water then my belief will be true, and hence satisfied, if and only if Socrates drinks water. The questions we are asking now are, What features constitute the components of the thought that Socrates drinks water, and how do those component elements relate the agent to the total thought and to the external world?

Everybody agrees that each component, “Socrates” and “water,” makes a contribution to the total truth condition of the thought. “Socrates” picks out Socrates and “water” refers to water.

There are then two sets of questions about the components of the thought. First, how does each element relate to the condition that it determines and second, how does the agent relate to the determination of those conditions? Granted that “Socrates” refers to Socrates and “water” refers to water, how does the agent have to relate to these words in order that he can use them to determine the conditions of satisfaction of the whole thought? The traditional answer, and the answer given by common sense, is that each word sets the condition it does because of its meaning and the agent is able to use the words the way he does because he knows the meaning of each of the words. And knowing the meaning enables him to use the word in such a way as to introduce the corresponding condition into the truth conditions of the entire sentence.

The question is, Is the condition associated with the word something that is represented in the speaker’s mind / brain, or is it something that is in part independent of the speaker’s mind / brain? According to the internalist, the condition must be represented in the speaker’s head. According to the externalist, the contents of the head are insufficient for successful reference. That is what Putnam meant when he said “Meanings just ain’t in the head.”

If we reject the externalist’s claim that intentional content is determined by external causal chains, what then does determine intentional content? Causally speaking, I do not think there is any general answer to this question except to say that our intentional contents are determined by a combination of our life experiences and our innate biological capacities. I have already given a sketch of how an animal’s feeling of thirst might be determined by neurobiological processes. If one were to change the example slightly so that I was not just thirsty in general but thirsty for a glass of draught Irish stout, or a 1953 Chateau Lafitte, then the story would become much more complicated. I would have to give an account of how my life experiences have led me to have certain sorts of taste experiences, that I was capable of recalling these in memory and capable of forming desires to repeat these experiences in the future. But if the story has to be more complicated to account for a specific desire, then it would become incredibly complicated if I tried to give an account of how one might have formed an intention with the content that I write the great American novel, marry a Republican, or explain intentionality in a single chapter.

The next step in nailing this whole account down to the real world is to point to the central role of consciousness. To have an intentional state consciously, for example to think consciously that Caesar crossed the Rubicon, is to be consciously aware of the conditions of satisfaction. To have the same intentional state unconsciously is to have something that is in principle is at least capable of becoming conscious. I will discuss the relation of the conscious and unconscious in detail in chapter 9.

If you ask, How can a state of my brain have the content that Caesar crossed the Rubicon? it seems an impossibly difficult question. But if you ask, How can my conscious thought “Caesar crossed the Rubicon” have the content that Caesar crossed the Rubicon? Then it is no longer impossible to answer. I know the meanings of the words, I know how they relate to objects and states of affairs in the world and in thinking the whole thought I am aware that it has precisely this condition of satisfaction: Caesar crossed the Rubicon. Once we reject the metaphysical sense of the third question we demystify it by assimilating it to a general account of how intentionality actually functions. And that is all that needs to be said about the constitution of intentional content in general. Beyond that, of course, we need to say a great deal, much of which I have already said, about the network and the background, about the direction of fit and causal self-referentiality, psychological mode, and all the rest of it.

I will spell out the relations between consciousness and intentionality in chapter 9. For the moment, just this: one huge evolutionary advantage of human consciousness is that we can coordinate a large amount of intentionality (“information”) simultaneously in a single unified conscious field. Think of the amount of coordinated intentionality (“information processing”) when, for example, you drive to work in the morning. Don’t just think of the coordination of perception and action. (For example, I am passing the car on my right. There is a red light ahead.) Think also of the constant accessing of unconscious intentionality. (For example, I will be late for my 9:00 a.m. appointment. Where shall I have lunch? I wonder how the meetings will go.) All of these are intentionalistic representations of the world, and we cope with the world by way of these representations.

Unless we presuppose some sort of uniformity of nature, the uniformity of nature guaranteed by causality and causation, we have no ground for inductive arguments. But, and this is the crucial point, there is no ground for the belief in the uniformity of nature, because any such a belief would have to be grounded in induction, which in turn would have to be grounded in the uniformity of nature; and thus the attempt to ground the belief in the uniformity of nature would be circular.

This felt determination of the mind gives us the conviction that there are necessary connections in nature. But that conviction is nothing but an illusion. The only reality is the reality of priority, contiguity, and constant conjunction. Causation on Hume’s account is literally just one damn thing after another. The only point is that there is a regularity in the way one thing follows another, and this regularity gives us the illusion that there is something more. But the necessary connection we think exists in nature is entirely an illusion in the mind. The only reality is regularity.