At Home: A Short History of Private Life

by Bill Bryson

Perhaps the most extraordinary clergyman of all was the Reverend Thomas Bayes, from Tunbridge Wells in Kent, who lived from about 1701 to 1761. Bayes was by all accounts a shy and hopeless preacher, but a singularly gifted mathematician. He devised the mathematical equation that has come to be known as Bayes’s theorem and that looks like this: People who understand Bayes’s theorem can use it to work out complex problems involving probability distributions—or inverse probabilities, as they are sometimes called. It is a way of arriving at statistically reliable probabilities based on partial information. The most remarkable feature of Bayes’s theorem is that it had no practical applications without computers to do the necessary calculations, so in Bayes’s own day it was an interesting but fundamentally pointless exercise. Bayes evidently thought so little of his theorem that he didn’t bother to make it public. In 1763, two years after Bayes’s death, a friend sent it to the Royal Society in London, where it was published in the society’s Philosophical Transactions with the modest title of “An Essay Towards Solving a Problem in the Doctrine of Chances.” In fact, it was a milestone in the history of mathematics. Today Bayes’s theorem is used in modeling climate change, predicting the behavior of stock markets, fixing radiocarbon dates, interpreting cosmological events, and doing much else where the interpretation of probabilities is an issue—and all because of the thoughtful jo...