Is the brain's mind a computer program?

C an a machine think ? Can a ma­ chine have conscious thoughts in exactly the same sense that you and I have? If by "machine" one means a physical system capable of performing certain functions (and what else can one mean?), then hu­ mans are machines of a special biolog­ ical kind, and humans can think, and so of course machines can think. And, for all we know, it might be possible to produce a thinking machine out of different materials altogether-say, out of silicon chips or vacuum tubes. Maybe it will turn out to be impossible, but we certainly do not know that yet. In recent decades, however, the question of whether a machine can think has been given a different inter­ pretation entirely. The question that has been posed in its place is, Could a machine think just by virtue of im­ plementing a computer program? Is the program by itself constitutive of thinking? This is a completely differ­ ent question because it is not about the physical, causal properties of actu­ al or possible physical systems but rather about the abstract, computa­ tional properties of formal computer programs that can be implemented in any sort of substance at all, provided only that the substance is able to carry the program. A fair number of researchers in arti­ ficial intelligence (AI) believe the an­ swer to the second question is yes; that is, they believe that by designing the right programs with the right in­ puts and outputs, they are literally