Sir Harold Jeffreys and His Cat: A Painting and a Painful Anecdote

May 14 - 2025

Recently I commissioned a painting of Sir Harold Jeffreys (1891–1989), whose groundbreaking Bayesian work remains a constant source of inspiration to me personally. The painting is now hanging in my office overlooking the chaos below, but I want to share it with the world as well. The painter is Marlijn Bouwman, and the painting is available under a CC-BY license (and available from the artwork library on this site). Here it is:

The presence of the cat is explained by an anecdote recounted by Mervyn Stone, who once escorted Jimmie Savage to the home of Harold Jeffreys and recalls the subsequent meeting between these early Bayesians as “a strange encounter in which Jeffreys had been largely silent, stroking his cat through what was far from a meeting of minds!” (Stone, 2013, p. 140). I believe Jeffreys could have had even more of an impact on the field if he had been more outgoing. Mind you, this is the person who invented the “conditional on” sign, who discovered the Bayesian hypothesis test, and who introduced invariant prior distributions, Bayesian mixture models, Bayesian model averaging, the symmetric Kullback-Leibler divergence (avant la lettre), the BIC (avant la lettre), and many other key concepts. Essentially, in the 1930s Jeffreys was the only Bayesian statistician in the entire world with an interest in practical data analysis.