“When you encounter the claim that all knowledge must derive from our senses, you should point out the anti-metaphysical objector that:
First, the anti-metaphysical claim is self-contradictory. How can we know that “all knowledge must derive from our senses?” This claim is not found in the objective world of sense experience. Have you ever sensed it in the real world? It is a non-material, mental construct. This sort of self-refuting argument illustrates Paul’s statement “they became futile in their speculations” (Rom. 1:21).
Second, the anti-metaphysical claim is presuppositional in nature. The claim does not allow for any empirical verification since it deals with the totality of reality because it asserts that “all knowledge must derive from our senses” (yet no man can comprehend all of reality) and is necessarily so in that it requires that “all knowledge must derive from our senses” (therefore it is not a truth dependent on the changing circumstances of the sense experience world of science). In the final analysis, this claim is a dogmatic assertion rather than an empirical conclusion.
Third, the anti-metaphysical claim destroys the very possibility of science. As we will explain in more detail later, science absolutely depends upon the uniformity of nature (so that experiments under controlled conditions can produce predictable results everywhere) and the assurance that the future will be like the past (so that experiments can predict future results). These two metaphysical claims allow scientists to generalize and project. Consequently, any anti-metaphysical complaint undermines science itself.
Fourth, the anti-metaphysical claim destroys reason. Empirical learning and reasoning would be impossible without these and other metaphysical assumptions. As we noted earlier, epistemology depends upon metaphysics. To evaluate arguments requires that we employ propositions, logical relations, and so forth. And these are not discovered through the senses, even though they are necessary to reason itself.”
(Bahnsen, Pushing the Antithesis, 127)