“Bayes’ theorem is to the theory of probability what the Pythagorean theorem is to geometry” – Sir Harold Jeffrey1 Good ol’ Jeffrey. There is a lot of truth to this statement, as Bayes’ theorem has formed the basis of a large part of Bayesian probability. What really is it though and what can it be used for? Well, it moves away from the traditional probability that you might know and focuses on using uncertainty to its advantage. “

Source: http://www.machinephilosopher.com/introduction-bayes-theorem/