Since the time of Plato's Theatetus, philosophers such as Plato's Socrates have asked the question: what is propositional knowledge? Merely believing something is insufficient for knowledge because anyone can believe anything without any further stipulations than that the subject accepts the belief. Even if the beliefs in question are true, knowledge still seems to require more than a simple approximation to truth by an accepted belief. Plato's solution to this problem was to develop three conditions for the transmission of belief into knowledge: justification, truth, and belief. Since Plato, a number of thinkers have developed critiques of this paradigm that account for different criticisms of it. I build on the work of a contemporary epistemologist named Alvin Goldman who in his seminal work Epistemology and Cognition developed a radical new concept of justification called process reliabilism. Process reliabilism claims that S knows that p only if S's belief in p results from a reliable belief-forming cognitive process. As a result of this work, a debate sparked in contemporary analytic epistemology between what are traditionally called the internalists and the externalists. Internalists claim that the determiners of justification must be internal to the epistemic agent, whereas externalists claim that external reliability is the sole determiner of justification. In the second chapter of this work, I provide an analysis of this debate and subsequently argue for the externalist position against a number of contemporary thinkers who seek to collapse the distinction. In the final section of this thesis, I incorporate research from experimental cognitive psychology and neuroscience to update the research cited by Goldman in Epistemology and Cognition.