[There is] a widespread approach to ideas which Objectivism repudiates altogether: agnosticism. I mean this term in a sense which applies to the question of God, but to many other issues also, such as extra-sensory perception or the claim that the stars influence man’s destiny. In regard to all such claims, the agnostic is the type who says, “I can’t prove these claims are true, but you can’t prove they are false, so the only proper conclusion is: I don’t know; no one knows; no one can know one way or the other.”
The agnostic viewpoint poses as fair, impartial, and balanced. See how many fallacies you can find in it. Here are a few obvious ones: First, the agnostic allows the arbitrary into the realm of human cognition. He treats arbitrary claims as ideas proper to consider, discuss, evaluate—and then he regretfully says, “I don’t know,” instead of dismissing the arbitrary out of hand. Second, the onus-of-proof issue: the agnostic demands proof of a negative in a context where there is no evidence for the positive. “It’s up to you,” he says, “to prove that the fourth moon of Jupiter did not cause your sex life and that it was not a result of your previous incarnation as the Pharaoh of Egypt.” Third, the agnostic says, “Maybe these things will one day be proved.” In other words, he asserts possibilities or hypotheses with no jot of evidential basis.
Peikoff here misrepresents agnosticism. He equates agnosticism with the creed of “I don’t know” and “Anything is possible." Is Peikoff right in his description of agnosticism? Perhaps we should turn to some actual agnostics to find out. And there is no better witness to call to the stand than the man who originally coined the term, Thomas Henry Huxley. Here is Huxley’s description of agnosticism:
Agnosticism … is not a creed, but a method, the essence of which lies in the rigorous application of a single principle. That principle is of great antiquity; it is as old as Socrates; as old as the writer who said, "Try all things, hold fast by that which is good" it is the foundation of the Reformation, which simply illustrated the axiom that every man should be able to give a reason for the faith that is in him; it is the great principle of Descartes; it is the fundamental axiom of modern science. Positively the principle may be expressed: In matters of the intellect, follow your reason as far as it will take you, without regard to any other consideration. And negatively: In matters of the intellect do not pretend that conclusions are certain which are not demonstrated or demonstrable. That I take to be the agnostic faith, which if a man keep whole and undefiled, he shall not be ashamed to look the universe in the face, whatever the future may have in store for him.
Now many Objectivists will protest Huxley’s use of the word faith, but here it is important to understand that Huxley is not advocating a blind faith (he was scientist, after all) but a justified faith—justified by the fruits of experience. Huxley understands that you cannot prove your starting points; that you have to begin with faith and then see how it works out. If your faith is corroborated by experiential trials that you subject it to, you are justified in keeping fast to it. Otherwise, you try something else. Agnosticism, then, for Huxley is simply the critical method of thinking. It means always keeping an open mind to new evidence. As Huxley puts it: “The results of the working out of the agnostic principle will vary according to individual knowledge and capacity, and according to the general condition of science. That which is unproven today may be proven by the help of new discoveries to-morrow. The only negative fixed points will be those negations which flow from the demonstrable limitation of our faculties. And the only obligation accepted is to have the mind always open to conviction.”
“Do not block the path of inquiry!” insisted philosopher C. S. Peirce. This is the great danger for those who believe that knowledge, in order to be useful, must be "certain:" that they will close their minds to new evidence, because, after all, the debate is over, certainty has been achieved! The path to inquiry is blocked by the de facto dogmatism of all claims to certainty. All Huxley’s agnosticism is trying to insist upon is to keep the mind open, keep the path to inquiry clear.
Peikoff mischaracterizes agnosticism as insisting on the proof of negatives. But that’s not in the least true. Agnosticism is merely pointing out that lack of evidence does not constitute proof that something doesn’t exist. This is not the same thing as saying that the all things are possible. Nor is it claiming we can’t have any beliefs or suspicions about extra-empirical entities such as the God of the Bible. There is nothing contradictory in an agnostic saying he doesn’t believe in that sort of God. But he doesn’t regard this belief as “certain” and determined for all time. The agnostic remains a steadfast fallibilist. He remains open to any new evidence that might be brought forth on the question. And so, when the agnostic H. L. Mencken was asked what he would do if, following his earthly demise, he suddenly found himself confronted by the twelve apostles, he answered: “I would simply say, ‘Gentlemen, I was mistaken.’”