AGRIPPA'S TRI-LEMMA

Consider a familiar skeptical problem. According to the skeptic, all know­ledge must be grounded in good reasons. But not any reason is a good ­reason – one must have reasons for believing that one's reasons are true. But then this insures that any attempt to ground knowledge in good reasons must be inadequate. For either (a) one's reasons will go on in an infinite regress, (b) they will come back in a circle, or (c) they will end arbitrarily. But none of these outcomes is satisfactory – none provides knowledge with grounding in good reasons. And therefore, the skeptic concludes, knowledge is impossible.

Externalism in general, and reliabilism in particular, has an easy answer to the problem. In fact, many would say, the answer is too easy. Let us first review what the answer is, and then consider why some have thought that the answer is too easy.

THE RELIABILIST'S REPLY

According to reliabilism, knowledge is true belief resulting from a reliable process, details aside. The details might include a clause to handle Gettier problems, and perhaps a clause restricting what sort of reliable process can ground knowledge. But none of these details will affect the essentials of the reliabilist account: knowledge is (essentially) true belief resulting from a reliable process. But then reliabilism has an easy answer to the skeptical reasoning reviewed above. Namely, the reliabilist can deny the first assumption of that reasoning – that all knowledge must be grounded in good reasons.