How Did Alan Turing Propose to Test Whether a Computer Can Think?
How Did Alan Turing Propose to Test Whether a Computer Can Think?
Editors’ Note: This is the third in a series of four esssays on Alan Turing, who is considered the father of modern computing. These essays are by Jack Copeland, an expert on Turing’s life and work.
How could researchers tell if a computer—whether a humanoid robot or a disembodied supercomputer—is capable of thought? This is not an easy question. For one thing neuroscience is still in its infancy. Scientists don’t know exactly what is going on in our brains when we think about tomorrow’s weather, or plan out a trip to the beach—let alone when we write poetry, or do complex mathematics in our minds. But even if we did know everything there is to know about the functioning of the brain, we might still be left completely uncertain as to whether entities without a human (or mammalian) brain could think. Imagine that a party of extraterrestrials find their way to Earth, and impress us with their mathematics and poetry. We discover they have no organ resembling a human brain; inside they are just a seething mixture of gases, say. Does the fact that these hypothetical aliens contain nothing like human brain cells imply that they do not think? Or is their mathematics and poetry proof enough that they must think—and so also proof that the mammalian brain is not the only way of doing whatever it is that we call thinking?Of course, this imaginary scenario about aliens is supposed to sharpen up a question that’s much nearer to home. For alien, substitute computer. When computers start to impress us with their poetry and creative mathematics—if they don’t already—is this evidence that they can think? Or do we have to probe more deeply, and examine the inner processes responsible for producing the poetry and the mathematics, before we can say whether or not the computer is thinking? Deeper probing wouldn’t necessarily help much in the case of the aliens—because ex hypothesi the processes going on inside them are nothing like what goes on in the human brain. Even if we never managed to understand the complex gaseous processes occurring inside the aliens, we might nevertheless come to feel fully convinced that they think, because of the way they lead their lives and the way they interact with us. So does this mean that in order to tell whether a computer thinks, we only have to look at what it does—at how good its poetry is—without caring about what processes are going on inside it?
That was certainly what Alan Turing believed. He suggested a kind of driving test for thinking, a viva voce examination that pays no attention at all to whatever causal processes are going on inside the candidate—just as the examiner in a driving test cares only about the candidate’s automobile-handling behavior, and not at all about the nature of the internal processes that produce the behavior. Turing called his test the “imitation game,” but nowadays it is known universally as the Turing test.