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human behaviour: The makeup of intelligence

The second major theory of the mind, functionalism, defines types of mental states in terms of their causal roles relative to sensory stimulation, other mental states, and physical states or behaviour. Pain, for example, might be defined as the type of neurophysiological state that is caused by things like cuts and burns and that causes mental states such as fear and “pain behaviour” such as saying “ouch.” Functionalism avoids the second objection against the type-type identity theory mentioned above—that it seems possible for two people to be in the same mental state but not in the same neurophysiological state—because it is not committed to the idea that the neurophysiological state that plays the causal role of pain must be the same in all people, or the same in people as in nonhuman creatures. This point was often expressed by saying that functional states exhibit “multiple realizability.”

Functionalism was inspired in part by the development of the computer, which was understood in terms of the distinction between hardware, or the physical machine, and software, or the function that the computer performs. It also was influenced by the earlier idea of a Turing machine, named after the English mathematician Alan Turing. A Turing machine is an abstract device that receives information as input and produces other information as output, the particular output