Strong AI

Notice that the thesis of [strong AI] is not that for all we know the collection of beer cans might be thirsty but rather that if it has the right program with the right input and output it must be thirsty (or understand Proust or worry about its income tax or have any other mental state) because that is all the mind is, a certain kind of computer program, and any computer made of anything at all running the right program would have to have the appropriate mental states.

I believe that everything we have learned about human and animal biology suggests that what we call “mental” phenomena are as much a part of our biological natural history as any other biological phenomena, as much a part of biology as digestion, lactation, or the secretion of bile. Much of the implausibility of the strong AI thesis derives from its resolute opposition to biology; the mind is not a concrete biological phenomenon but “an abstract sort of thing.”

Still, in calling attention to the implausibility of supposing that the specific causal powers of brains are irrelevant to minds I have not yet fully exposed the preposterousness of the strong AI position, so let us press on and examine a bit more closely the thesis of mind as program.

Digital computer programs by definition consist of sets of purely formal operations on formally specified symbols. The ideal computer does such things as print a 0 on the tape, move one square to the left, erase a 1, move back to the right, etc. It is common to describe this as “symbol manipula- tion” or . . . the whole system as a “self-updating representational system“; but these terms are at least a bit misleading since as far as the computer is concerned the symbols don’t symbolize anything or represent anything. They are just formal counters.

The computer attaches no meaning, interpretation, or content to the for- mal symbols; and qua computer it couldn’t, because if we tried to give the computer an interpretation of its symbols we could only give it more unin- terpreted symbols. The interpretation of the symbols is entirely up to the pro- grammers and users of the computer. For example, on my pocket calculator if I print “3 � 3 �,” the calculator will print “9” but it has no idea that “3” means 3 or that “9” means 9 or that anything means anything. We might put this point by saying that the computer has a syntax but no semantics. The computer manipulates formal symbols but attaches no meaning to them, and this simple observation will enable us to refute the thesis of mind as program.