The British mathematician Alan Mathison Turing (1912-1954) was noted for his contributions to mathematical logic and to the early theory, construction, and use of computers.

# Alan Mathison Turing

Alan Turing was born in London, England, on June 23, 1912. Both his parents had upper middle class origins, and his father continued that tradition as an administrator in the Indian civil service. With his father off in India, Turing was sent away to private boarding schools. After some early problems with social adjustment, he distinguished himself in mathematics and science.

Turing's exceptional mathematical abilities were first generally recognized in his college years (1931-1936) at King's College of Cambridge University. His most important mathematical work, "On Computable Numbers, " was written in Cambridge in 1936. In this paper Turing answered a question of great significance to mathematical logic— namely, which functions in mathematics can be computed by an entirely mechanical procedure. His answer was phrased in terms of a theoretical machine (today known as the "Turing machine") which could mechanically carry out these computations. Embodied in the Turing machine idea is the concept of the stored program computer.

In 1936 Turing was awarded a Proctor fellowship to visit Princeton University for a year. There he came in contact with Alonzo Church, a professor of mathematics working on problems in logic related to those addressed by Turing in his 1936 paper. He decided to remain at Princeton an additional two years to write a doctoral dissertation under Church's direction on ordinal logics.

Soon after Turing's return to England Britain was drawn into World War II. He joined the Government Code and Cypher School in Bletchley Park, located between Oxford and London, where a massive effort was underway to break German codes which had been encyphered by machine. Turing played an important role (still partly classified) in the design of equipment and development of techniques to break these codes.

Work at Bletchley provided Turing with valuable experience in electronics and with special-purpose calculating equipment which served him well after the war. In 1945 he moved to the National Physical Laboratory (NPL) in Teddington, England, to assume responsibilities for designing an electronic computer to be used in government work. Turing drew up plans for the ACE computer, an ambitious stored program computer utilizing vacuum tubes for switching and mercury delay lines for storage. A scaled down version completed in 1950, known as Pilot ACE, was one of the earliest operating stored program computers. Pilot ACE served many important functions, including aircraft design, for many years.

Meanwhile, dissatisfied with progress on his project at NPL, Turing accepted a position at Manchester University where a large computer, the Mark I, was being built. His position as chief programmer of the Mark I allowed him the opportunity to program the computer to do mathematics, play chess and other games, investigate automatic language translation, and do cryptanalysis. This was probably the first major attempt to use a stored program computer for non-computational activities.

Turing's work on computers influenced the design of early computers built by the English Electric and Bendix companies. However, of more enduring significance were his theoretical contributions to automata theory and artificial intelligence. The 1936 paper and the concept of the Turing machine is the starting point of the modern theory of automata, and Turing anticipated many of the fundamental questions. During and after the war Turing began to investigate and champion the field of artificial intelligence. To his credit are the Turing Test (a test for determining whether a machine can be claimed to be thinking), a series of papers arguing against the most common objections to the possibil-ity of intelligent machinery, and the recognition that scientists should approach the problem of artificial intelligence through the programming of stored program computers rather than through the construction of robots that mimic human actions. Turing also made a number of other contributions to mathematical logic, algebra, statistics, and morphogenesis (the study of biological forms).

Turing died in his home in Manchester, England, of cyanide poisoning. His death, ruled to be suicide by the coroner, may have been the result of a depression caused by chemotherapy. The courts had mandated this treatment as a result of his conviction for public practice of homosexuality, then a criminal offense in Britain.

## Further Reading on Alan Mathison Turing

Two biographies of Turing have been written: a short study by his mother, Sara Turing, *Alan M. Turing* (1959), and a longer study by Andrew Hodges, *Alan Turing: The Enigma* (1983). Hodges cites references to Turing's published paper and other secondary literature about him.

## Additional Biography Sources

Hodges, Andrew, *Alan Turing: the enigma,* New York: Simon and Schuster, 1983.