Abstract: In this chapter, I examine a priori knowledge from the perspective of my account of warrant. According to the epistemological tradition, what is known a priori is known, somehow, prior to or independently of experience; in the first section of this chapter, I attempt to clarify this claim and describe some of the general features of a priori belief and knowledge. In the second section I argue, among other things, that a priori warrant (more precisely, intuitive warrant) is fallible and comes in degrees. I go on to consider an objection to the existence of a priori knowledge based on what has been called the causal requirement (roughly, the claim that any objects of which we have knowledge must be such that we stand in an appropriate causal relation with them). I argue that there is no plausible form of the causal requirement that constitutes a good objection to the existence of a priori knowledge; along the way, I offer an argument for the conclusion that propositions cannot be concrete objects of any sort, and point out that it is quite possible to think of abstract objects as capable of standing in causal relations with us.

Keywords: a priori, abstract objects, belief, causal requirement, concrete objects, fallibility, intuitive warrant, propositions, warrant,