Rationalism is the view that intuitions are a defeasible source of non-inferential justification. The first part of this dissertation is an exposition and defense of this view. I begin with an account of what it is for a proposition to seem true, arguing that seemings are a sui generis, irreducible propositional attitude that is importantly related to, yet distinct from, perceptual, memorial, and introspective experiences. I then defend the view that intuitions are seemings of a certain sort. I argue that seemings generally, and thus intuitions in particular, are a defeasible source of non-inferential justification, and I defend the epistemic value of seemings and intuitions against various objections. The second part of my dissertation ass...