Traditionally, the three fundamental laws of logic: (1) the law of contradiction, (2) the law of excluded middle (or third), and (3) the principle of identity.
That is, (1) for all propositions p, it is impossible for both p and not p to be true (symbolically, 00AC; (p 2227; 00AC; p)); (2) either p or not p must be true, there being no third or middle true proposition between them (symbolically p 2228; 00AC; p); and (3) if a propositional function F is true of an individual variable x, then F is true of x (symbolically, ( 2200; x) [F(x) 2283; F(x)]). Another formulation of the principle of identity asserts that a thing is identical with itself, or ( 2200; x) (x = x).