Despite occasional evidence to the contrary, I have persisted in the belief that the ability to play chess well indicates a powerful intelligence. Goethe wrote that chess was a touchstone of the intellect, while Pascal called it the gymnasium of the mind. Arthur Koestler romanticised the mental power of chess devotees, writing: ‘When a chess player looks at the board, he does not see a static mosaic, a “still life”, but a magnetic field of forces, charged with energy — as Faraday saw the stresses surrounding magnets and currents as curves in space; or as Van Gogh saw vortices in...