According to Interest-Relative Invariantism, whether an agent knows that p, or possesses other sorts of epistemic properties or relations, is in part determined by the practical costs of being wrong about p. Recent studies in experimental philosophy have tested the claims of IRI. After critically discussing prior studies, we present the results of our own experiments that provide strong support for IRI. We discuss our results in light of complementary findings by other theorists, and address the challenge posed by a (...) leading intellectualist alternative to our view. (shrink)