We begin as philosophers where we began as babies, at the only place there is to begin: by looking at the world. As philosophers, however, we know enough to state, as we look at anything: it is. This (I am pointing to a table) is. That (pointing to a person seated at it) is. These things (sweeping an arm to indicate the contents of the whole room) are. Something exists.
We start with the irreducible fact and concept of existence—that which is.
The first thing to say about that which is is simply: it is. As Parmenides in ancient Greece formulated the principle: what is, is. Or, in Ayn Rand’s words: existence exists. (“Existence” here is a collective noun, denoting the sum of existents.) This axiom does not tell us anything about the nature of existents; it merely underscores the fact that they exist.3
This axiom must be the foundation of everything else. Before one can consider any other issue, before one can ask what things there are or what problems men face in learning about them, before one can discuss what one knows or how one knows it—first, there must be something, and one must grasp that there is. If not, there is nothing to consider or to know.
The concept of “existence” is the…
Read the rest in Objectivism: The Philosophy of Ayn Rand.