Technology & Medicine › Electric age › Electronic computer (Z3, Colossus, ENIAC)
Alan Turing
1912–1954; 'On Computable Numbers' 1936· Person· Communication & computing
Well documentedSolid records, physical evidence or scientific consensus.
Alan Turing, an English mathematician, defined in theory what a computer is and helped break German codes in World War II.
See it on the Technology & Medicine map →How it works
In 1936 Turing described an imaginary 'universal machine' that reads and writes symbols on a tape by following rules, and showed it could carry out any calculation that can be written as steps. At Bletchley Park he designed the Bombe, an electromechanical machine that found the daily Enigma settings. After the war he designed the ACE computer and in 1950 proposed the 'imitation game', now called the Turing test. Prosecuted for homosexuality in 1952, he died of cyanide poisoning in 1954.
Why it mattered
His idea that one machine can do any task, given the right instructions, underlies all software. Computing's top prize is the Turing Award.
Legacy and how we know
His 1936 paper 'On Computable Numbers', his 1950 paper in Mind and declassified Bletchley files. Britain apologized in 2009, pardoned him in 2013 and put him on the £50 note.
Still unknown or debated
His death was ruled suicide; some scholars, including Jack Copeland, argue it may have been accidental cyanide inhalation from home chemistry experiments.
Connections (3)
▸Alan Turing laid the theory of the Electronic computer (Z3, Colossus, ENIAC)Well documented
The connection
Turing's 1936 'universal machine' showed in theory that one machine could do any computable task if fed the right instructions. That idea, plus his wartime codebreaking machines, fed into postwar stored-program computers; he designed Britain's ACE (1945) and wrote programming guides for Manchester's computers.
When and how
Cambridge, 1936; Bletchley Park, 1939–45; National Physical Laboratory, London (ACE design, 1945–47); Manchester University, 1948–54.
How we know
His papers and reports survive; John von Neumann knew Turing's 1936 paper, and his 1945 stored-program design report reflects similar ideas.
Debates and open questions
How much Turing's theory actually shaped ENIAC's engineers and von Neumann's design, versus independent practical thinking, is still debated among historians.
▸Alan Turing proposed the test now applied to Large language modelsMostly agreed
The connection
In his 1950 paper 'Computing Machinery and Intelligence', Turing proposed the 'imitation game': if a judge chatting by text cannot reliably tell a machine from a person, the machine can fairly be said to think. For 70 years no program passed convincingly; large language models are the first to hold long, humanlike conversations, reviving the test.
When and how
Turing at the University of Manchester, 1950, in the journal Mind; modern tests by researchers such as Cameron Jones and Benjamin Bergen at UC San Diego, 2023–25.
How sure are we?
Turing's paper is published; in a 2025 UC San Diego study, judges picked GPT-4.5 as the human 73% of the time in five-minute chats.
Debates and open questions
Many experts argue that passing the test shows convincing imitation, not real understanding; whether it was ever a good measure of intelligence is debated.
▸Alan Turing rebutted the 'Lady Lovelace objection' of Ada LovelaceWell documented
The connection
Lovelace wrote that the Analytical Engine 'has no pretensions whatever to originate anything' and could only do what it was ordered. In his 1950 paper 'Computing Machinery and Intelligence', Turing named this 'Lady Lovelace's Objection' and argued machines could surprise us and might, in principle, learn.
When and how
London, 1843 (Lovelace's Note G); Manchester, 1950, published in the philosophy journal Mind.
How we know
Both texts survive and are widely reprinted; Turing quotes her directly.
Debates and open questions
Whether today's AI systems truly 'originate' anything or only recombine their training data is the same debate, still unresolved.