# 6.3.1 Axioms of Probability

**Axiom I****:**The probability of an event happening positive, or zero. $P[A]\leq0$**Axiom II:**The total (added) probability of each event in a set is equal to one. $P[S]=1$**Axiom III:**If two subsets have no elements in common, then the probability of the two sets combined into one set is the individual probability of the individual sets added together. $\text{If } A\cap{B}= \emptyset\text{ then } P[A\cup{B}] = P[A]+P[B]$