Somehow I convinced myself I'd like to understand Bayes' theorem better.
P(A|B) = P(A)P(B|A)/P(B)
where A and B are events.
P(A) and P(B) are the probabilities of A and B without regard to each other.
P(A|B), a conditional probability, is the probability of A given that B is true.
P(B|A), is the probability of B given that A is true.