Alan Turing

Alan Turing (1912 to 1954) was a British mathematician and logician whose work laid theoretical foundations for computer science. During World War II he helped break German Enigma ciphers at Bletchley Park, and in 1950 he proposed a test for machine intelligence. He was convicted in 1952 under laws that criminalized homosexuality, and he was granted a royal pardon in 2013.

Early life of Alan Turing

Turing was born in Paddington, London, on June 23, 1912. He entered Sherborne School in 1926, and during the general strike of that year he cycled about 60 miles to reach it. He later became a fine long-distance runner.

An event in 1928 deeply affected him. His close friend Christopher Morcom died in February 1930, and the experience was shattering for Turing. Despite difficult school years, his talent was clear. He sat the Cambridge scholarship examinations in 1929 and won an exhibition, though not a scholarship. He entered King’s College, Cambridge, in 1931 to study mathematics and graduated in 1934.

In 1933 he became interested in mathematical logic, and in the spring of 1935 he attended Max Newman’s course on the foundations of mathematics. In 1935 he was elected a fellow of King’s College for a dissertation on the central limit theorem, a result in probability theory.

Career and major work of Alan Turing

In 1936 Turing wrote On Computable Numbers, with an Application to the Entscheidungsproblem. The paper showed that no general procedure can decide every mathematical question, a result reached independently by the American logician Alonzo Church. It appeared in print in 1937, and from 1936 to 1938 Turing studied at Princeton University under Church and earned a doctorate.

When war was declared in 1939, Turing moved to the Government Code and Cypher School at Bletchley Park. With Gordon Welchman he developed the Bombe, a machine based on earlier work by Polish mathematicians. From late 1940 it was used to decode messages sent on the Enigma machines of the German air force.

By the middle of 1941 his statistical methods, together with captured material, had led to the decoding of German navy signals. Andrew Hodges, Turing’s biographer, writes that the breaking of U-boat Enigma helped save the Battle of the Atlantic. This work is part of the history of cryptography and of codebreaking more broadly. Between November 1942 and March 1943 Turing was in the United States to help coordinate decoding work and to study a speech secrecy system.

After the war he moved to the National Physical Laboratory in London, and in March 1946 he submitted a report proposing the Automatic Computing Engine, or ACE. He returned to Cambridge in 1947 and 1948, then joined the University of Manchester, where Newman offered him a readership. In 1951 he was elected a Fellow of the Royal Society.

Ideas and contributions of Alan Turing

Turing’s best-known idea is the Turing machine, an imaginary device that reads and writes symbols on a tape according to a fixed table of rules. In his 1936 paper he proved that a universal machine could exist, one that can imitate any other such machine when given its description. This is the theoretical basis of the stored-program computer, and the algorithm as a step-by-step procedure became precise through this work.

In 1950 he published Computing Machinery and Intelligence in the journal Mind. The paper proposed what is now called the Turing test, in which a person converses with a hidden human and a hidden machine and tries to tell them apart. It remains a reference point in discussions of artificial intelligence, although researchers disagree about how useful it is as a measure.

Late in his life he turned to biology and published work on a non-linear theory of how biological forms grow. In the early 1950s he was also exploring problems in physics and biology that he left unfinished.

Conviction, death and pardon

In 1952 Turing was arrested as a homosexual, at a time when such acts were crimes in Britain, and he lost his security clearance. Security officers worried that someone with detailed knowledge of work at GCHQ had become a security risk, and they began to investigate his foreign visitors.

Turing died on June 7, 1954, at Wilmslow, Cheshire, of cyanide poisoning. An inquest concluded that the poison was self-administered, although his mother always maintained that his death was an accident. People affected by thoughts of suicide can find help through local crisis services.

In September 2009 the British Prime Minister, Gordon Brown, issued a public apology for the way Turing had been treated. On December 24, 2013, he was given a posthumous pardon under the Royal Prerogative of Mercy, at the request of the Justice Secretary, Chris Grayling. The government noted a long campaign that included an e-petition and the support of scientists such as Stephen Hawking.

Legacy of Alan Turing

Turing is often called a founder of computer science. His 1936 work made the idea of computation precise, and later engineers built machines whose design reflects it. The Association for Computing Machinery names its highest award in his honor.

His wartime work is often credited with shortening the war, although historians stress that Bletchley Park depended on thousands of people and on Polish groundwork. Official secrecy kept much of the effort hidden until the 1970s, which delayed public recognition of what he and his colleagues achieved. The wartime effort also shaped later work in signals intelligence.

Today his name appears on buildings, prizes, scholarships and public statues, and his life story has been told in books, plays and films. His treatment is now widely regarded as an injustice, and the 2013 pardon is part of how Britain has acknowledged that.

Editorially reviewed by Specialty Digest Editorial TeamLast reviewed November 4, 2026Researched and drafted with AI assistanceReport an issue