In the commonly accepted language of logic, “certain” refers to the conclusions we reach using deductive logic. For example, once the rules of an arithmetic are decided on, 2 + 2 = 4 every time we do it; i.e., it is “certain”. In the 17th century, David Hume found that inductive logic cannot be certain; we cannot know the sun will rise tomorrow, just because it came up yesterday. Hume’s knowledge of the world through inductive logic is “probable”. This is commonly called, “the Problem of Induction”.
Rand has written a straw man on this topic, which she ascribes to David Hume, “Don’t be so sure, nobody can be certain of anything.”i
This essay covers the second sentence of Rand’s attempted refutation, “The pronouncement means no knowledge of any kind is possible to man; i.e., that man is not conscious.”
Rand’s philosophy of Objectivism is based on tabula rasa , the idea that sensory data makes a one-to-one impression of reality in our minds. “Conscious” means to be aware of your senses. By using the single law of her logic, A = A, we recognize similarities in the things we observe. That is “knowledge”.
For Rand, inductive logic and deductive logic are both the same logic of A = A, just working in different directions. Once we have a concept built from observation (inductive), we may or may not assign new observations to that concept (deductive).
Rand’s Objectivist Epistemology applies these ideas to every human’s mind. Since we all observe the same reality and logic is consistent, all our mental concepts are the same. People who claim to disagree with Rand’s concepts must be ignorant or telling deliberate lies.
Hume’s finding that deductive knowledge and inductive knowledge are separate and distinct; and that knowledge gained through observations and inductive logic is “probably” right and possibly wrong, contradicts every aspect of Rand’s philosophy. If Hume is right, Rand’s “objective” philosophy is just her personal interpretation of her sensory impressions. Her concepts are just “probable”. People can honestly disagree with her without being evil.
So, Rand uses her logic of “non-contradictory identification”. If her philosophy, considering inductive reasoning as certain, leads to her definition of knowledge; then Hume’s philosophy must lead to no knowledge at all. If Rand is “conscious” using her philosophy, Hume’s philosophy must lead to unconsciousness. Since those things are not possible, Hume must be an evil person spreading deliberate lies.
More footnotes are needed!
i paragraph 10, Chapter 2, Philosophical Detection; Philosophy Who Needs It? by Ayn Rand