“COUNTEREXAMPLES” TO MODUS PONENS: LOGICAL CORRECTNESS AND EPISTEMIC RATIONALITY

Abstract

The paper deals with the epistemological problems posed by the application of the modus ponens rule in cognitive processing of distributed information. Distinguishing the deductive correctness of a rule of inference from its normativity for rational belief, we consider ‘counterexamples’ of modus ponens proposed in modern epistemology of logic that endanger not its model-theoretic validity, but epistemic rationality for boundedly rational cognitive agents. We explain the epistemic lacunas in the closure of knowledge according to modus ponens revealed by Dretske’s ‘counterexamples’ by a variety of standards of validity that go beyond ‘common sense’. However, the epistemic ‘counterexamples’ of modus ponens proposed by McGee, Kolodny, and MacFarlane require, in our opinion, an appeal to less obvious epistemic phenomena, which can be discovered by reasoning for interpretation. We demonstrate that the supposed ‘counterexamples’ to modus ponens do not conflict with either the epistemic neutrality of logic or its epistemic relevance to boundedly rational agents. On the contrary, the appeal to reasoning for interpretation, which is needed to resolve the difficulties caused by these ‘counterexamples,’ helps to achieve a balance between the epistemic constraints of reasoning agents and the logical requirements for the correctness of their interpretive and deductive cognitive operations.