Mind: A Brief Introduction (John R. Searle) / quote 62 of 138
Minds are like carburetors, thermostats and clocks
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.