Critics may complain that this set of principles is incomplete and sketchy. (Indeed, in spite of the principles about memory, nothing in this system even purports to explain how someone could have knowledge of the past.) Chisholm has given us no more than a sketch of a possible answer to the question of how empirical knowledge is possible. But it reveals the foundational, coherentist, Chisholmian epistemic principle-ist structure of his thought. All later variants retain these features. What is most distinctive about these principles is that they are not instances of more general logical principles and Chisholm does not claim that they are true in virtue of any facts about causal connections or reliability. They are presented as fundamental epistemological facts.