This paper traces the development of the idea that we must cultivate moral virtue in order to attain some degree of illumination regarding the nature of reality. I use the term “illumination” to cover a range of meanings intended by the philosophers I discuss, such as the “acquisition of wisdom” (Phaedo, 65a), the “sight” of divine beauty (Symposium, 210d–212b), or a mystical experience involving God or divine reality. Although this theme appears in many texts from the Platonic tradition, I focus on three major stages of its development. First, I show how Plato provides the basic framework of the idea that moral virtue is necessary for illumination, especially in his Phaedo and Symposium. Then, I explain how Plotinus synthesizes and substan...