1. The Law of Contradiction
   1. For all propositions p, it is impossible for both p and not p to be true.
2. The Law of Excluded Middle
   1. Either p or ∼p must be true, there being no third or middle true proposition between them.
3. The Principle of Identity
   1. If a propositional function F is true of an individual variable x, then F is true of x.
   2. A thing is identical with itself, simply that x is x.