Implicit in these discussions was the materialist view that there was no autonomous 'mind' or 'soul' which used the mechanism of the brain.
(He had perhaps hardened his stance as an atheist, and his conversation was more free with anti-God and anti-church jokes than it would have been before the war.)
To avoid philosophical discussions about what 'mind' or 'thought' or 'free will' were supposed to be, he favoured the idea of judging a machine's mental capacity simply by comparing its performance with that of a human being.
It was an operational definition of 'thinking', rather as Einstein had insisted on operational definitions of time and space in order to liberate his theory from a priori assumptions.
This was nothing new—it was an entirely standard line of rationalist thought.
Indeed in 1933 he had seen it on the stage, for in Back to Methuselah Shaw had a future scientist produce an artificial 'automaton' which could show, or at least imitate, the thought and emotions of twentieth century people. Shaw had the 'man of science' assert that he had no way of drawing a line between 'an automaton and a living organism'.
Again, his Natural Wonders book had accepted the rationalist view, with a chapter called 'Where some of the Animals do their Thinking' which treated thought, intelligence and learning as differing only in degree as between monocellular animals and human beings.
It was no new idea, therefore, when Alan talked in terms of an imitation principle: that if a machine appeared to be doing as well as a human being, then it was doing as well as a human being.
But it gave a sharp, constructive edge to their discussions.