Thomas Aquinas has long been understood to have reconciled faith and reason. Typically, he is understood as having provided justification for faith by means of proof, particularly, that the Five Ways prove the existence of God. Under this interpretation, faith becomes a species of justified belief, and the justification for faith rests upon the success of the Five Ways . In this dissertation, I argue that Aquinas' account of faith is not one of justified belief, at least as it is (...) understood in contemporary philosophy. Instead, I argue, faith has its own basis for epistemic "reasonableness"---a reasonableness that does not derive from ordinary evidence nor proof. Rather than requiring evidence accessible to the natural light of reason, Aquinas holds that faith has its own sort of "evidence"---that which results from the light of faith. Aquinas "Aristotelianizes" faith and argues that faith has the Aristotelian epistemic virtue of certitude, and in so doing reconciles faith and Aristotelian reason, at least as Aristotle was understood by Medieval philosophers. This reconciliation resolves important tensions between Aristotelian science and Christian doctrine. Further, I examine three contemporary accounts of what counts as an epistemically "responsible" belief and argue that under Aquinas' account, faith should be counted as rational, and in an important, though modified sense, as justified. (shrink)