This paper is concerned with a well-known problem concerning the retention of propositional knowledge. Although most of what we currently believe ourselves to know originates in the past, we usually do not know how we originally acquired that knowledge. But then, on what grounds can we still know it? In this paper, I outline two different types of approaches to the problem in light of notable epistemic theories, and then examine difficulties faced by them.
2010 The Philosophy of Science Society, Japan