The Probability of Faith

Thomas Baynes was the minister of the Presbyterian Chapel in the English spa town of Tunbridge Wells from around late 1733. By all accounts he was a better mathematician than he was a church minister. As a non-conformist, he was prevented from attending the English universities, so he began to study in 1719 at Edinburgh University in Scotland. A number of years later, he published a work entitled "Divine Benevolence," and in 1742, he was made a fellow of the Royal Society after defending Isaac Newton against Bishop Berkeley in a 'pamphlet war.' Bayes did work with fluxions, infinite series, and probability. In the late 1740s, Bayes set out his theory of probability that eventually bore his name. His theorem was discovered after his death. It had no practical applications in his lifetime, and was therefore never published. It was his fellow mathematician and church minister Richard Price who discovered it among Bates' effects aftee his death and submitted it for publication as "An Essay Towards Solving a Problem in the Doctrine of Chances." A man named Laplace later rediscovered and modified it into a form we largely recognize today. McGrayne Bayes writes "In discovering its value for science, many supporters underwent a near-religious conversion yet had to conceal their use of Bayes' rule and pretend they employed something else. It was not until the 21st-century that the method lost its stigma and was widely and enthusiastically embraced." Today it is used among other things to forecast weather, identify e-mail spam, improve lowres images on computers, and determine forgeries. The formula known today is: P(A I B) = [P(B I A) x P(A)] / P(B) where P(A) denotes the probability of A and P(A I B) is the probability of A given that B has occurred. 

Interestingly, Bayes' theorem has been used by philosophers of religion such as Richard Swinburne to try and prove God's existence and by other such as philosopher John Mackie and the atheist evangelist Richard Dawkins in an attempt to disprove God's existence.