Commutativity is a replacement rule in sentential logic that says that P ^ Q is equivalent to Q ^ P, P v Q is equivalent to Q v P, and P <=>] Q is equivalent to Q <=> P. In each commutativity case, you are swapping the order of a statement that has a symmetric operator. (Note that you cannot commute a regular implication because implications are not symmetric like conjuctions are.) You might already be familiar with their mathematical cousins, like 1 + 2 = 2 + 1. It is the same principle here.