One information-processing system, differently programmed, can simulate many quite different information-processing systems. Which suggests that a computer, suitably programmed, might be able to simulate the information-processing systems found in the nervous systems of biological creatures. Certain results in abstract computing theory lend strong support to this expectation. If a given computer meets certain functional conditions, then it is an instance of what theorists call a universal Turing machine.…The interesting thing about a universal Turing machine is that, for any well-defined computational procedures whatever, a universal Turing machine is capable of simulating a machine that will execute those procedures. It does this by reproducing exactly the input/output behavior of the machine being simulated. And the exciting fact is, the modern computer is a universal Turing machine. (One qualification: real computers lack unlimited memories. But memory can always be made larger to meet demand.) This is the deeper sense…in which modern digital computers are “general-purpose” machines.

The question that confronts the research program of AI, therefore, is not whether suitably programmed computers can simulate the continuing behavior produced by the computational procedures found in natural animals, including those found in humans. That question is generally regarded as settled. In principle, at least, they can. The important question is whether the activities that constitute conscious intelligence are all computational procedures of some kind or other. The guiding assumption of AI is that they are, and its aim is to construct actual programs that will simulate them.