Rand's philosophy begins with three axioms: existence, consciousness, and identity.[11] Rand defined an axiom as "a statement that identifies the base of knowledge and of any further statement pertaining to that knowledge, a statement necessarily contained in all others whether any particular speaker chooses to identify it or not. An axiom is a proposition that defeats its opponents by the fact that they have to accept it and use it in the process of any attempt to deny it."[12] As Objectivist philosopher Leonard Peikoff argued, Rand's argument for axioms "is not a proof that the axioms of existence, consciousness, and identity are true. It is proof that they are axioms, that they are at the base of knowledge and thus inescapable."[13]