Mind: A Brief Introduction (John R. Searle) / quote 27 of 138
Descartes denies that animals have minds
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.