The most fundamental axiom of Aristotle’s metaphysics is the principle of non-contradiction. It can be stated in several ways, but they all convey the same essential idea, namely, that something cannot both be and not be in the same way. A number cannot be both odd and not odd, a man cannot be both alive and not alive, and something cannot both exist and not exist. In a way, this principle gives us an absolute knowledge of all things, for within it is the concept of being simply along with its distinction from non-being, which is being’s negation. Any knowledge of being simply, though, must necessarily be a knowledge of all that is since being is, by definition, what is.