Alan Turing: The Enigma
Author: Andrew Hodges | Published: 1983
Summary
Alan Turing: The Enigma is the definitive biography of Alan Turing—mathematician, logician, cryptanalyst, and one of the founders of computer science—written by mathematician and Turing scholar Andrew Hodges. The book traces Turing’s life from his unhappy schooling at Sherborne to his foundational work in mathematical logic (the 1936 paper on computable numbers and the Turing machine), his crucial contributions to breaking the Enigma cipher at Bletchley Park during WWII, his work on early digital computers at Manchester and NPL, and his tragic death in 1954—officially ruled a suicide by cyanide poisoning following a court-ordered chemical castration for “gross indecency” (homosexual conduct). Hodges writes with the authority of a mathematician who can explain the technical work and the sympathy of someone who spent years recovering a story that Turing’s society had deliberately suppressed.
The technical sections—on the incompleteness theorem and its relationship to Turing’s decision problem, on the Turing machine as a formal model of computation, on the Bombe machines that exploited Enigma’s vulnerabilities—are among the clearest explanations of these subjects in any biography; Hodges does not simplify them for non-technical readers but builds them up carefully from first principles. The Bletchley sections reconstruct not only the cryptographic achievements but the organizational culture of the place—the mix of brilliant eccentrics, the strict secrecy, the creative atmosphere—that produced them. Hodges is particularly good on what was actually accomplished: he estimates that the Bletchley codebreaking shortened the war in Europe by two years.
The biographical context—Turing’s experience as a gay man in a society that criminalized his sexuality, his relationship with Christopher Morcom (his first love, who died in adolescence), his refusal to conceal or apologize for his sexuality, and his eventual prosecution—runs through the book as an undercurrent that occasionally becomes the main current. Hodges wrote the biography in 1983 when Turing’s homosexuality was still considered too sensitive for public discussion; the book was partly an act of recovery and vindication. The 2009 UK government apology and 2013 royal pardon of Turing came in part from the cultural work this biography accomplished.
Critical Takeaways
- Turing’s foundational contributions: The biography establishes Turing’s claims clearly: the theoretical foundations of computability (the Turing machine), the practical foundations of WWII codebreaking (the Bombe), and the early work on machine intelligence (the Turing test) are all documented with technical precision.
- Bletchley Park and WWII: Hodges’s estimate that Bletchley’s work shortened the war by two years—with corresponding reduction in casualties—places Turing’s contributions in a scale that even non-technical readers can assess.
- The state’s crime: The biography is also a sustained indictment of the British state’s treatment of Turing: a man who may have done more than anyone else to secure the Allied victory was prosecuted, chemically castrated, and driven to suicide for his sexuality. The moral reckoning is unambiguous.
- The Turing Test: Hodges’s treatment of the Imitation Game (now called the Turing Test) as a philosophical provocation rather than a practical test is more careful than many subsequent accounts; he situates it within Turing’s broader interest in the question of machine intelligence.
- Legacy: The book contributed significantly to the rehabilitation of Turing’s reputation; it preceded the public disclosure of Bletchley Park’s work (still classified when Hodges began writing) and relied partly on sources that would soon become more accessible.
My Takeaways
- The Turing machine—the abstract theoretical model of computation—being developed in 1936 as a solution to a mathematical logic problem, years before any physical computer existed, showed me that the most practically consequential ideas are often developed without any practical intent.
- The Bletchley sections gave me a model for interdisciplinary intellectual work under pressure: mathematicians, linguists, chess players, and engineers solving problems that required all their different competencies simultaneously.
- The tragedy of Turing’s prosecution is not simply individual injustice but institutional stupidity: the state persecuted one of its most valuable servants for a characteristic that was entirely irrelevant to his service. The waste is as enraging as the injustice.
- The Turing Test is often misunderstood as a test for consciousness; Hodges helped me see it as Turing’s provocative reformulation of an unanswerable metaphysical question into an answerable behavioral one. The philosophical move is the interesting part.