The Law of Identity

Implicit in the axioms of existence and consciousness is the law of identity: A is A. To be is to be something as against other things. The "identity" of an existent refers to that which it is, the sum of its attributes or characteristics---its nature. The fact identified here is subtly different than that identified in the axiom of existence: the latter distinguishes something from nothing, the former distinguishes this thing from that thing.

This law is, along with existence and consciousness, an axiom: a fundamental and inescapable starting point of knowledge. Wherever a man is studying something, he is studying something as against some other thing. The "thing" is the identification.