Gushing waterfall over rocks on a rainy day

Definitions and Explanations


The Principle of Identity states that each thing is identical with itself.  This is a fancy way of saying that a given thing is not another thing.  It is expressed mathematically as 1 = 1 or A = A.  The Principle of Identity is directly related to the Principle of Non-Contradiction.  The Principle of Identity is fundamental to mathematics and logic and, subsequently, truth.  Why?  If we lose the basis for rationale thinking, we can no longer accurately say much about anything.

Photo by Ivana Cajina from