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Alan Turing (Part I - his life and achievements)

Updated: Mar 27, 2023

By John Coss, Vice Chair of Stockport Humanists

Continuing our series of profiles of humanists who are not as widely known as they should be, including distinguished men and women not generally known to be humanists.

Alan Turing - a founding father of computing and AI


Alan Turing (1912-54) was eminent in mathematics, including statistical theory and cryptology, and made important contributions to logic and philosophy of mind. He is generally regarded as one of the founding fathers of computing and artificial Intelligence. Through his work as a code breaker at Bletchley Park he made a vital contribution to the war effort in Britain during the Second World War, by some accounts on par with those of Churchill and Eisenhower. Turing also made an important contribution to mathematical biology. And he was a serious runner, who might well have represented Great Britain in the marathon at the 1948 Olympic Games. A gay man, he was convicted of gross indecency in 1952, and undertook a course in hormone treatment as an alternative to imprisonment. He died from cyanide poisoning, with a half-eaten apple beside his bed. The coroner’s verdict was suicide, though some think his death was accidental. An alternative view is that he did intentionally take his own life, but arranged this in a way that enabled his mother to believe his death was accidental.

An atheist, Turing could not square religious faith with the commitment to reason and logic which propelled his life and career. But he remained passionately interested in the world and its apparent mysteries, and awake to the possibilities of the human mind and the power of collaboration. In the words of his biographer Andrew Hodges, his was ‘a life seeking freshly minted answers to fundamental questions.’

When he died, Turing was hardly known outside the fields in which he had worked, and his death attracted little public attention. The code breaking at Bletchley Park was still top secret, and few people knew anything about computers. One cannot help wondering what else he might have achieved during a normal life span. This month, I focus on his life and work. In the April issue, for which the theme is Power People – those who shape our destiny, I will review developments since his death as his achievements came to be recognised.

Early work in maths and computing

Turing was a student at King’s College, Cambridge from 1931 and was elected a Fellow in 1935 (aged 23), based on a dissertation that proved a version of the Central Limit Theorem, a key element of probability theory (though unknown to Turing, this had already been proved a few years earlier). In 1936, his paper On Computable Numbers, with an Application to the Entscheidungsproblem (a German word meaning 'decision problem') was published in the Proceedings of the London Mathematical Society. In providing a definitive answer to this ‘decision problem’ in mathematics, he developed the concept of what became known as the Universal Turing Machine, which is the foundation of the modern theory of computation and computability, and hence of the computer age. There are now over four billion Turing Machines in the world, which we call computers; and there are several billion more in smart phones and other devices.

Turing then spent two years at Princeton University, where he was a doctoral student of Alonzo Church, who had separately solved the Entscheidungsproblem and made other important contributions to computer science. Turing also met John von Neumann, who later made fundamental contributions to the development of computer architecture. Church and von Neumann are also widely regarded as founding fathers of computing and artificial intelligence. While at Princeton, Turing applied his practical bent to the construction of a machine based on using electromagnetic relays to multiply binary numbers.

German Enigma machine

Bletchley Park code-breaking

Turing returned to Cambridge in 1938, and secretly worked part-time for the Government Code and Cypher School. On the outbreak of World War II in September 1939, he took up full-time work at its Bletchley Park headquarters, where he made indispensable contributions to a substantial team effort. Initially, the key task of the code-breakers was to decipher messages encrypted by German Enigima machines. Fortunately, they were able to draw on Polish work in the years preceding the War on earlier versions of Enigma, which was shared with their French and British allies in July 1939. The first version of the Bombe – an electro-magnetic device designed by Turing that replicated the action of several Enigma machines wired together and greatly helped decipher Enigma messages – was developed in late 1939 and operational in early 1940. An improved version with refinements devised by Gordon Welchman was working by August 1940. For a while in 1942-3, naval messages encrypted by an enhanced form of Enigma machine could not be deciphered, and Allied shipping in the Atlantic suffered severe losses, but while Turing was in America engaged in high level liaison on encryption, logical weaknesses in the new system were detected, and effective decryption restored for the rest of the War.

Colossus (on the left) and Lorenz (on the right) - public domain images

Bletchley Park engaged in decryption of other messages, including Japanese, Italian and Soviet messages. Of particular note is the Colossus codebreaking computer – developed to help decipher the Lorenz-encrypted (Tunny) messages between Hitler and his generals during World War II. (British cryptanalysts, who referred to encrypted German teleprinter traffic as 'fish', called the machine and its traffic 'Tunny' - meaning tuna fish.) This was mainly designed by Tommy Flowers of The Post Office Research Station, though Turing’s use of probability in cryptanalysis contributed to its design. It was arguably the first electronic computer, despite lacking some essential features of modern computers. By this time, Turing was effectively a consultant on all Bletchley Park activities. At the end of the War, there were some 10,000 personnel working there, and Eisenhower expressed his heartfelt admiration and sincere thanks to all at Bletchley Park for ‘their very decisive contribution to the Allied war effort’.

Post war: the 'imitation game'

After the war, Turing worked on the design of the Automatic Computing Engine (ACE) at the National Physical Laboratory, and in 1946 he wrote a paper on the design of an electronic stored program computer. Drawing on his code breaking work during the war and practical pioneering of the first electronic computers, Turing argued that all the operations of the mind could be performed by computers. His thesis is the cornerstone of modern Artificial Intelligence.

In 1949, Turing became the deputy director of the Computing Laboratory at the University of Manchester: he was their first software specialist and focused on the software needed to drive the Manchester Mark 1 stored program computer, one of the first recognisably modern computers.

In 1950 Turing published Computer Machinery and Intelligence, in which he sought to address the question ‘can machines think?’. Instead of doing so directly, he proposed an alternative approach, which he called the ‘imitation game’, related to a then popular game played by three people: a man (A), a woman (B), and an interrogator (C) in a separate room. The object of the game is for C to determine which of A and B is a woman, and which is a man, based on their answers to a series of questions, where their aim is to mislead C. Turing asks 'What will happen when a machine takes the part of A in this game? and then poses the question: ‘Will the interrogator decide wrongly as often when the game is played like this as he does when the game is played between a man and a woman?’ In effect, this is asking if machines can do what we (as thinking entities) can do. Turing himself suggested some alternative procedures, and other variants have since been proposed. There remains much debate, e.g. here, about the relevance of the Turing Test today, but it still stands as a philosophical starting point for discussing and researching AI and defining intelligence, and what we should expect from technologies for them to be considered thinking machines.

In 1952, Turing wrote The Chemical Basis of Morphogenesis, which describes how patterns in nature, such as stripes and spirals can arise naturally. They are now known as Turing patterns and his theory has become a basic model in theoretical biology, which uses mathematical models and analyses and representations of living organisms to examine the systems that govern structure, development, and behaviour of and within biological systems.

This was his final publication before his tragic death in 1954. At the time, he was virtually unknown to the public. The steps toward his posthumous recognition are the subject of Part II of this profile, which will be published in the April edition of Humanistically Speaking.

"At some stage, we should expect the machines to take control." Alan Turing

Turing quotations

Although all of these quotes have been attributed to Turing, some actually come from fictionalised versions of him, for example in the film The Imitation Game, including the first shown here.


Sometimes it is the people no one can imagine anything of who do the things no one can imagine.

We can only see a short distance ahead, but we can see plenty there that needs to be done.

Thinking is a function of man's immortal soul. God has given an immortal soul to every man and woman, but not to any other animal or to machines. Hence no animal or machine can think.

I am unable to accept any part of this, but will attempt to reply in theological terms. I should find the argument more convincing if animals were classed with men, for there is a greater difference, to my mind, between the typical animate and the inanimate than there is between man and the other animals.

I am not very impressed with theological arguments whatever they may be used to support. Such arguments have often been found unsatisfactory in the past. In the time of Galileo it was argued that the texts, 'And the sun stood still... and hasted not to go down about a whole day' (Joshua x. 13) and 'He laid the foundations of the earth, that it should not move at any time' (Psalm civ. 5) were an adequate refutation of the Copernican theory. With our present knowledge such an argument appears futile. When that knowledge was not available it made a quite different impression.

The popular view that scientists proceed inexorably from well-established fact to well-established fact, never being influenced by any unproved conjecture, is quite mistaken. Provided it is made clear which are proved facts and which are conjectures, no harm can result. Conjectures are of great importance since they suggest useful lines of research.

It is not possible to produce a set of rules purporting to describe what a man should do in every conceivable set of circumstances.

A computer would deserve to be called intelligent if it could deceive a human into believing that it was human.

On the use of decrypted information

When we want to sink a convoy, we send out an observation plane first... Of course, to observe is not its real duty, we already know exactly where the convoy is. Its real duty is to be observed...Then, when we come round and sink them, the Germans will not find it suspicious.

On computers

It is possible to invent a single machine which can be used to compute any computable sequence.

The idea behind digital computers may be explained by saying that these machines are intended to carry out any operations which could be done by a human computer.

On Artificial Intelligence

What we want is a machine that can learn from experience.

I believe that at the end of the century the use of words and general educated opinion will have altered so much that one will be able to speak of machines thinking without expecting to be contradicted.

If a machine is expected to be infallible, it cannot also be intelligent.

It seems probable that once the machine thinking method had started, it would not take long to outstrip our feeble powers… They would be able to converse with each other to sharpen their wits. At some stage therefore, we should have to expect the machines to take control.

No, I'm not interested in developing a powerful brain. All I'm after is just a mediocre brain, something like the President of the American Telephone and Telegraph Company.


Humanist Heritage article on Turing

A short biography by Andrew Hodges

An Introductory Biography also by Hodges, based on a talk to mark what would have been Turing’s 90th birthday

Bletchley Park: Alan Turing FAQs

Comments on Turing quotes


There are many, often conflicting, accounts of the contributions of various individuals to the early development of computers and AI, and to the code breaking work at Bletchley Park. I have tried here to present a fair view of Turing’s achievements: see this 2014 article from BBC Future.

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