Posterior Probability Expresses the likelihood of an Event given some observed evidence and can be calculated with P(a∣b)=P(a∧b)P(b)P(a\mid b)=\frac{P(a\land b)}{P(b)}P(a∣b)=P(b)P(a∧b) where P(b)≠0.P(b) \neq 0.P(b)=0. Intuition: The likelihood of having aaa and bbb, within the set of Outcomes where we have bbb. See Bayes Theorem Prior Probability Likelihood Evidence Conditional Probability Distribution