Subject-Sensitive Invariantism and Isolated Secondhand Knowledge

Jennifer Lackey challenges the sufficiency version of the knowledge-action principle, viz., that knowledge that p is sufficient to rationally act on p, by proposing a set of alleged counterexamples. Her aim is not only to attack the knowledge-action principle, but also to undermine an argument for subject-sensitive invariantism. Lackey holds that her examples are counterexamples to the sufficiency version of the knowledge-action principle because (a) S knows the proposition in question, but (b) it is not rational for S to act on it. In this paper, first, I argue against (a) on intuitive and on theoretical grounds. Second, I point out that (b), even if combined with (a), is not sufficient to make for counterexamples to the knowledge-action principle of the relevant kind. Third, I offer two alternative explanations of the intuition Lackey relies on. If either one of them is right, (b) may not be satisfied in her examples.