that if a statement implies a statement and a statement also implies , then if either or is true, then has to be true. The reasoning is simple: since at least one of the statements P and R is true, and since either of them would be sufficient to entail Q, Q is certainly true.

An example in English:
:1. If I'm inside, I have my wallet on me.
:2. If I'm outside, I have my wallet on me.
:3. It is true that either I'm inside or I'm outside.
:Therefore, I have my wallet on