Alan Turing, who played a decisive role in breaking the German Enigma cipher at Bletchley Park during the Second World War, had already in his 1936 paper described the "Turing machine" — the theoretical computing device that became the mathematical foundation of modern computer science. In 1950, at the University of Manchester, in an age when most people had never seen a computer, he asked a more provocative question: can machines think?

Turing conceded that the question itself was vague — "thinking" lacks a clear definition. So he proposed a game, the "imitation game." A questioner converses through written text with two hidden subjects — one human, one machine. If the questioner cannot tell which is which, no behavioural ground remains to deny the machine "thinks." This move — replacing a philosophical question with a measurable performance — was the real power of the test.

Turing took on the counter-arguments one by one in the paper: the theological objection ("only humans have souls"), the mathematical objection (Gödel), the consciousness argument, the argument from intuition, and others. He answered each in turn. He predicted that by 2000 machines would be able to pass the test; this has happened in part — today's large language models can fool humans in limited settings, while the question of "general intelligence" remains open.

Turing was prosecuted in 1952 for homosexuality and forced to undergo chemical castration; he died in 1954 at the age of 41, of cyanide poisoning. The test that bears his name became the framing question for the field of artificial intelligence which John McCarthy and his colleagues would formally establish at Dartmouth in 1956 — and it is still argued over 75 years later.