In my last post, we saw how Leonard Nelson argues that a theory of knowledge is impossible in his paper “The Impossibility of the ‘Theory of Knowledge’.” Next, Nelson gives an analysis of why the project of constructing a theory of knowledge turned out to be impossible. (He claims to be following Kant’s method of analyzing the presuppositions of a problem before trying to solve the problem itself.)

The first step Nelson takes is to point out that “theory of knowledge” assumes that the validity of cognition is questionable. I think what he means is that projects like Descartes’ attempt to prove the validity of sensory perception assume that sensory perception is capable of being questioned in the first place. (The point is broader than just attempts to prove the validity of sensory perception, though.) So Nelson wants to investigate this assumption that anyone can question the objectivity of cognition.

Nelson identifies the assumption that we can question the objectivity of cognition as an instance of the “logical principle of sufficient reason, according to which every assertion needs a verification.” Nelson seems to be thinking of verification as justification, i.e., some sort of prior reason to think that the assertion is true. Since not every assertion can be proven by reducing it to other assertions, there must be a method of verification in addition to proof.

What method might this be? Nelson claims that, in addition to the combinations of concepts which are judgments, we also have immediate, non-conceptual perceptual knowledge. We combine concepts into judgments and try to get them to match our perceptions. While it is not guaranteed that our judgments will match our perceptions and therefore be true, it is guaranteed that our perceptions are veridical – indeed, perception cannot be questioned as such.

To summarize, I think what Nelson is saying is that the “theory of knowledge” gets into trouble because it ignores the possibility of a criterion of knowledge which is validated, not by reducing it to other propositions, but by direct perception. If that is what he is saying, then I’m not sure why he isn’t just running into the same problem he set for the “theory of knowledge”: To know that direct perception is a valid source of knowledge, he would have to directly perceive that direct perception is a valid source of knowledge, which presupposes that direct perception is a valid source of knowledge. So, it will be interesting to see what Nelson has to say about that, if anything.

I should also add that I do not see how Nelson has proven that the validity of cognition is not questionable. He has asserted that we have perceptual judgments which are unquestionable, but this seems question begging against the “theory of knowledge” that he is criticizing. It’s possible that he will defend this claim later in his paper.