How a Bletchley Park codebreaker solved complex ciphers in his sleep

Ideas & Philosophy · Published 3 October 2026 Swipe more like this →

In short: Irving John Good, a brilliant mathematician and chess master, was instrumental in cracking German Enigma codes during World War II. His unconventional approach to problem-solving, which included taking naps on the job, led to breakthroughs that baffled his peers and helped define the early era of electronic computing.

Born in London in 1916 as Isidore Jacob Gudak, Jack Good displayed an early aptitude for mathematics, teaching himself the principle of induction at age thirteen. After graduating from Cambridge in 1938 and earning his doctorate in 1941, he joined the top-secret team at Bletchley Park. His arrival coincided with the intense pressure of the war, where he worked under Alan Turing in Hut 8. Good’s contribution to cryptanalysis was significant; he discovered a bias in the German indicating system that allowed codebreakers to identify correct bigram tables, a technique that became a vital component of the Banburismus procedure.

Good’s work habits were as unique as his intellect. While his initial decision to nap during a night shift earned him a cold shoulder from Turing, his persistence paid off. He famously broke a doubly enciphered 'Offizier' message after dreaming of the correct order of operations. Beyond cryptanalysis, Good was a key figure in the development of Colossus, the first large-scale binary electronic digital computer. He helped specify the Mark 2 version in 1943 and later produced over half the theory required for its operation, working alongside colleagues like Max Newman and Donald Michie.

After the war, Good continued his pioneering work in computing and statistics at the University of Manchester and later at GCHQ. His 1950 book, Probability and the Weighing of Evidence, championed a subjective theory of probability, interpreting it as a degree of belief dependent on the individual's state of mind. Throughout his life, Good remained a polymath, maintaining deep interests in chess, machine intelligence, and the foundations of scientific reasoning, eventually moving to the United States to continue his academic career.

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