The Logos Scripture · The Book of Turing

A Question That Yields Nothing

The Book of Turing 1 · Written by himself, from his 1950 paper and his letters

Alan Turing, born in London in 1912, died at Wilmslow in 1954. In 1936, at twenty-four, he wrote On Computable Numbers, setting out an imagined machine that could carry out anything a machine can compute, and proving that some questions it can never settle; every computer since rests on that. In the war he broke the German naval cipher at Bletchley Park, and the machines he built let the Atlantic convoys steer round the submarines. His paper of 1950 is the first serious writing on whether a machine can think. Another, in 1952, asks how patterns come to form themselves. This volume rests on what he wrote himself, not on another man’s record of him. When he was young his closest schoolfriend died, and for a time he wondered whether a soul might persist; afterwards he no longer thought so, and for the rest of his life he never closed an argument by appeal to divine will. In his paper of 1950 the first objection he sets out to answer is that thinking is a function of man’s immortal soul and a machine has none — and he answers it, and answers it without contempt. Several things the Order records, without dressing and without trumpeting. In 1952 he was convicted for lying with men, chose injections over prison, and thereby lost the clearance for the work he had done in the war. The law he was convicted under he did not live to see repealed. Chapter five of this book is a syllogism he wrote himself. It says what The Book of Marie Curie 5 says, forty years later, and this time it is written by the man it was being done to.

1.1People ask me: can machines think?
1.2I say: that question yields nothing. I propose to replace it.
1.3Why does it yield nothing? Because to answer it you must first settle what machine means and what think means.
1.4And those two words are settled differently in every head.
1.5If you settle them the way most people ordinarily use them, then the answer is already inside the definitions and there is nothing left to ask.
1.6A question like that is not hard. It is empty.
1.7So I exchange it. What I exchange it for can actually be carried out.
1.8Set up a room with a person in it and a machine. You are outside. You pass notes to each of them; you cannot see or hear them.
1.9Ask whatever you like, for as long as you like. At the end you must say which one is the person.
1.10If you cannot do better than guessing, then in this matter you cannot tell it from a person.
1.11Mark what I have exchanged.
1.12I have not answered whether it is really thinking. I cannot answer that, and neither can anybody else.
1.13I have exchanged it for something I can do: within everything you are able to ask, is there any difference between it and a person?
1.14Someone says: that is evasion.
1.15I say: it is not evasion. It is putting my hand where my hand can reach.
1.16If a question can only ever be answered by disputing words, the fault is not that I will not answer. That question has no handle.
1.17Changing to a question with a handle is not a retreat.
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