Out-Gunning Skepticism

Extract

Bredo C. Johnsen¹ misconceives my strictures concerning acceptance of the following principle (where ‘p’ stands for any empirical proposition):

(1) If A both knows that p and knows that p entails q, then A can come to know that q.

Johnsen seems unaware that my criticism was intended to apply only after (1) is made to appear in its most plausible light; that is, only after its consequent is interpreted as: ’It is logically possible for A to know that q.’ Without this interpretation (1) might be dismissed simply on the grounds that A suffers from some physical or psychological disability that prevents him from drawing inferences from what he knows.

Properly interpreted, (1) remains acceptable as long as the propositions substituted for p and q are such that it is at least logically possible for A to get evidence enough to make them known. Agreement on this point is itself enough to render Johnsen's own examples irrelevant. For instance, even though it may be physically impossible for A to get adequate evidence that in the constellation Andromeda there is a planet intermediate in size between Venus and Earth, the foregoing is still a fit substitution instance for q; but since such a q does not suffice to falsify the consequent of (1), it does nothing to generate any skeptical argument, either.