Abstract

Impurism says that practical factors encroach on knowledge. An important version of impurism is called ‘Threshold-Impurism,’ which says that practical factors encroach on the threshold that rational credence must pass in order for one to have knowledge. A prominent kind of argument for Threshold-Impurism is the so-called ‘principle-based argument,’ which relies on a principle of fallibilism and a knowledge-action principle. This paper offers a new challenge against Threshold-Impur- ism. I attempt to show that the two principles Threshold-Impurists are committed to—KJ and Fallibilism—are jointly in tension with a widely-held principle of credence that’s called ‘Truth-Directedness,’ in the sense that the former two principles cannot both apply to those who know the third. This tension constitutes a serious challenge to Threshold-Impurists, because it leaves them two options, both of which are undesirable: denying Truth-Directedness, or accepting Truth-Directedness and accepting that whether KJ and Fallibilism apply to a person depends on whether she knows Truth-Directedness.