Abstract

Externalist theories of knowledge often claim that whether a person's true belief is knowledge depends on the reliability of the faculties that produced the belief. Some philosophers think that the force of Cartesian skeptical arguments presents a problem for these theories. Externalism seems to entail a too-easy response to skepticism: since whether we know depends mainly on the reliability of our faculties, and skeptical arguments give us no reason to think our faculties unreliable, such arguments do not threaten our knowledge. Many have thought that the ease with which Externalists respond to skepticism should prompt us to reject their view. ;In my dissertation, I attempt to answer this objection by providing Externalists with a more plausible response to skepticism. My response borrows from Relevant Alternatives theories, which tell us when we have to be able to rule out alternatives to our beliefs in order for those beliefs to amount to knowledge. Such theories typically argue that far-fetched alternatives raised by the skeptic are not relevant, so our inability to rule them out does not deprive us of knowledge. RA theories have attracted attention recently for their purported success in responding to skepticism. I believe that two prominent RA theories should in fact be rejected, but that some RA insights should be adopted by Externalists. ;To show this, I first clarify what RA theories are, and spell out their differences. I then argue against two prominent RA theories. Against one, I defend the closure principle---the principle according to which knowledge is closed under known entailment. Against the other , I argue that we need not postulate that 'know' is a contextual term in order to explain the power of skeptical arguments. I then develop my own RA theory, which claims that when we encounter skeptical arguments, we often cease to believe propositions that we would otherwise know. I show how this theory can account for the power of skeptical arguments, and can helpfully be appended to Externalist theories of knowledge, to give them a more plausible response to skepticism.