Bayes Theorem Origins

In his book 'An Enquiry concerning Human Understanding'  David Hume posited that inherently fallible evidence is insufficient proof against natural laws - eyewitness testimony can’t prove a miracle. Bayes, a Presbytarian minister, motivated to rebut him was interested in understanding how much evidence would we need to be persuaded that something is a probability regardless of how improbable it is. He developed an equation that focuses on updating our beliefs with new evidence. His work, An Essay towards solving a Problem in the Doctrine of Chances, was reviewed by Richard Price after Bayes' death who believed that Bayes’ Theorem helped prove the existence of God.

When we are presented with new information, we can use Bayes’ Theorem to refine our pre-existing belief.  It is fairly easy to determine the probability of the effect given a cause. Since Bayes’ Theorem works in the reverse direction, many find it complicated.

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