Alan Turing

Agora

Alan Turing

1912–1954

A first way ina deliberate simplification – the portrait says more

Whatever can be computed by following rules step by step can be computed by one simple kind of machine – and instead of asking whether machines think, we should ask whether they can converse indistinguishably from a human.

Placement

Science & Human Sciences · Northern Europe · Mind & Consciousness, Logic, Science

Defined computability with the “Turing machine” (1936); in 1950 he proposed replacing the question “Can machines think?” with an imitation game – the Turing test – and so opened up the philosophy of artificial intelligence.

Key ideas

Turing machine
Universal machine and undecidability
Imitation game

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Influence

Influenced by 4

David Hilbert

influenced by
Turing answered Hilbert and Ackermann’s decision problem (Grundzüge der theoretischen Logik, 1928) in the negative, defining computability through his machines (‘On Computable Numbers’, 1936). A. M. Turing, “On Computable Numbers, with an Application to the Entscheidungsproblem” (1936–37); D. Hilbert and W. Ackermann, Grundzüge der theoretischen Logik (1928); SEP “Hilbert’s Program”; SEP “Alan Turing”
Evidence: AI draft
David Hilbert › 1862–1943
Bertrand Russell

influenced by
Turing studied Russell’s Introduction to Mathematical Philosophy in 1933, according to Hodges, and later adapted Russell’s theory of types (‘Practical Forms of Type Theory’, 1948). A. Hodges, Alan Turing: The Enigma (1983); A. M. Turing, “Practical Forms of Type Theory”, Journal of Symbolic Logic 13 (1948); B. Russell, Introduction to Mathematical Philosophy (1919)
Evidence: also in InPhO · InPhO
Bertrand Russell › 1872–1970
Ludwig Wittgenstein

influenced by disputed
Turing attended Wittgenstein’s Cambridge lectures on the foundations of mathematics (1939) and argued with him over contradictions; how far this shaped Turing’s work is disputed. C. Diamond (ed.), Wittgenstein’s Lectures on the Foundations of Mathematics, Cambridge, 1939 (1976); J. Floyd, “Turing on ‘Common Sense’: Cambridge Resonances”, in J. Floyd and A. Bokulich (eds.), Philosophical Explorations of the Legacy of Alan Turing (2017)
Evidence: AI draft
Ludwig Wittgenstein › 1889–1951
Kurt Gödel

influenced by
Turing related his unsolvability proof for the Entscheidungsproblem to Gödel’s incompleteness theorem and, like Gödel’s arithmetisation, coded machines as numbers (‘On Computable Numbers’, 1936). A. M. Turing, “On Computable Numbers, with an Application to the Entscheidungsproblem”, Proceedings of the London Mathematical Society 42 (1936–37); K. Gödel, Monatshefte für Mathematik und Physik 38 (1931); SEP “Alan Turing”
Evidence: AI draft
Kurt Gödel › 1906–1978

Influenced 4

Hilary Putnam

influenced
Putnam modelled mental states on the states of a Turing machine, founding machine functionalism (‘Minds and Machines’, 1960; ‘Psychological Predicates’, 1967). H. Putnam, “Minds and Machines”, in S. Hook (ed.), Dimensions of Mind (1960); “Psychological Predicates” (1967), repr. as “The Nature of Mental States”; SEP “Functionalism”
Evidence: also in InPhO · InPhO
Hilary Putnam › 1926–2016
Jerry Fodor

influenced
Fodor built his computational theory of mind on Turing’s model of computation: thinking is rule-governed manipulation of symbols in a language of thought (The Language of Thought, 1975). J. A. Fodor, The Language of Thought (1975); The Mind Doesn’t Work That Way (2000); SEP “The Computational Theory of Mind”
Evidence: AI draft
Jerry Fodor › 1935–2017
Daniel Dennett

influenced
Dennett defended Turing’s test as a fair criterion (‘Can Machines Think?’, 1985) and paired Turing with Darwin on competence without comprehension (From Bacteria to Bach and Back, 2017). D. C. Dennett, “Can Machines Think?” (1985), in Brainchildren (1998); From Bacteria to Bach and Back (2017); SEP “The Turing Test”
Evidence: also in InPhO · InPhO
Daniel Dennett › 1942–2024
Luciano Floridi

influenced
Floridi called Turing’s the fourth revolution after Copernicus, Darwin and Freud: we are informational organisms (‘inforgs’) among other intelligent agents (The Fourth Revolution, 2014). L. Floridi, The Fourth Revolution: How the Infosphere Is Reshaping Human Reality (2014); The Philosophy of Information (2011)
Evidence: AI draft
Luciano Floridi › b. 1964

Criticism

Criticized by 1

John Searle

criticised by
Searle’s Chinese Room targeted the Turing test as a criterion of understanding: a program passing it by symbol manipulation need not understand anything (‘Minds, Brains, and Programs’, 1980). J. R. Searle, “Minds, Brains, and Programs”, Behavioral and Brain Sciences 3 (1980), 417–457; A. M. Turing, “Computing Machinery and Intelligence”, Mind 59 (1950)
Evidence: AI draft
John Searle › 1932–2025

Works

1936On Computable Numbers, with an Application to the Entscheidungsproblem
Paper in the Proceedings of the London Mathematical Society: a machine that reads and writes symbols on a tape captures what a person calculating by a fixed rule can do; one “universal” machine can do the work of any other, and Hilbert’s decision problem has no mechanical solution – a result Alonzo Church reached at the same time by other means.
1950Computing Machinery and Intelligence
Can machines think? The imitation game.

Position

In 1936 Turing defined what it means for something to be computable by imagining a simple machine that reads and writes symbols on a tape. This “Turing machine” showed both the power and the limits of mechanical calculation – some problems can never be solved by any algorithm – and became the theoretical basis of the computer. In 1950 he asked whether machines can think and replaced the question with a test: if a machine can converse so that we cannot tell it from a human, we have no good reason to deny it intelligence. He answered many objections in advance, opening the philosophy of mind and of artificial intelligence.

Life & context

Born in London in 1912, Turing studied mathematics at King’s College, Cambridge, and completed a doctorate at Princeton. During the Second World War he played a leading role at Bletchley Park in breaking the German Enigma code. Afterwards he designed early computers in London and Manchester. In 1952 he was convicted of “gross indecency” because of a relationship with a man – sexual acts between men were then a crime in Britain – and given the choice between prison and probation on condition of hormone treatment; he accepted the treatment. He died in 1954 of cyanide poisoning, which the inquest ruled suicide. In 2009 the British government apologised, and in 2013 he received a posthumous royal pardon.