How does a man born blind conceptualize the color red? He lacks the sensory ability necessary to perceive color. He thus has no perception to apply logic to. He may accept on the authority of others that something called “red” exists. However, to him individually, the concept will only ever be what Rand called a “floating abstraction.” From Objectivism Wiki:
The fallacy of the “floating abstraction” is Ayn Rand’s term for concepts detached from existents, concepts that a person takes over from other men without knowing what specific units the concepts denote.
As we consider our hypothetical blind man, we recognize that a strict application of objectivist epistemology leaves him unable to claim that he knows there is a color red. Yet the color exists, not just as a concept but as a metaphysical reality. So we may conclude that reality, or that which exists, is not limited to that which can be perceived.
D’Souza made this point in his debate with Bernstein, noting that a person of the 5th century B.C. could only be aware of a fraction of the stars that we know of today. Our perception has been expanded by technology, increasing our range of knowledge. Yet all the stars exist whether we perceive them or not.
In fairness, Objectivism does not deny the existence of the unknown. It merely claims that knowing occurs through a rational process of applying logic to perception. Since the supernatural cannot be perceived, it cannot be known to exist. However, Objectivism does not stop at an agnostic skepticism. It claims to prove through logic that there is no god or supernatural realm of any kind. Bernstein spent the bulk of his speaking time on this point, offering up two fascinating arguments.
The first centered around the relationship between existence and consciousness. Bernstein reminded the UT audience that “existence exists,” which is the Aristotelian law of identity. A thing is what it is. He next evoked the law of causality, which says that a thing acts according to what it is. A glass of water behaves as a glass of water, and not as sulfuric acid. Bernstein then pointed out that consciousness is the faculty which perceives existence, and therefore is dependent upon existing. On the other hand, existence is independent of consciousness. A rock exists without knowing it.
Bernstein asserted that Christianity violates this basic principle known as the primacy of existence. Christianity starts with an all-knowing consciousness without existence, he claimed, pointing out that consciousness cannot create anything. “What does God create the universe from?” he asked. “If you start with nothing, you end with nothing? There is no God. There is no creation. The universe is eternal.”