In 2006 I visited Professor Emeritus John McCarthy in his little house on the outskirts of the Stanford University campus. It was almost exactly 50 years after McCarthy coined the term "artificial intelligence" at a conference on computers and problem resolution, and I wanted to ask him how he thought it went. Then, even when the subject was still in its infancy, the claims were hardly modest. One of the most prominent debaters, Marvin Minsky, said that we should be excited about the future in which we got to serve as housepets of the computers. Most scientists agreed that it was only a matter of time before computers became more intelligent than us, and "took over".

But what happened next? In one version of history, there followed 50 years of failure, where computers time and again proved unable to solve even simple problems. The human mind could not be captured in computer science algorithms. The dream, or nightmare, of artificial intelligence turned...