The Turing Test: A Question That Defined a Century

Alan Turing's 1950 paper "Computing Machinery and Intelligence" opens with a question: "Can machines think?" He then immediately sets it aside. "I propose to replace these questions," he writes, "with another, which is closely related to it and is expressed in relatively unambiguous words." What followed was the Imitation Gameand it was stranger than most people remember.

The original Imitation Game was not a machine pretending to be human. It was a machine pretending to be a woman pretending to be a man. Turing's setup: Interrogator C asks questions of two players, Player A (a man) who is trying to make C think he is a woman, and Player B (a woman) trying to help C correctly identify her. Now replace Player A with a machine. If the interrogator can't tell the difference, the machine has "passed." The gender component, widely dropped from the popular version, was Turing's original framing.

Turing predicted that by the year 2000, machines would be capable enough that an average interrogator would have less than a 70% chance of correctly identifying the machine within five minutes of questioning. He was roughly right on timeline, ALICE won the Loebner Prize repeatedly in the early 2000s, and Eugene Goostman "passed" a version of the test in 2014. Whether these represent "thinking" is another question.

The test has always been controversial. John Searle's Chinese Room argument (1980) contended that passing the Turing Test didn't imply understanding, a system could manipulate symbols correctly without any inner experience. Turing himself anticipated most philosophical objections in the original paper and addressed them with remarkable foresight. His section on "The Theological Objection," whether machines could have souls, is still worth reading.

Turing was arrested in 1952 for "gross indecency," consensual homosexual relations then illegal in Britain, and subjected to chemical castration. He died in 1954, aged 41, of cyanide poisoning. A coroner ruled it suicide. The man who asked whether machines could think was himself treated as less than human by the society he had helped save. Britain issued a formal apology in 2009. He received a posthumous royal pardon in 2013.