Sense-perception is a hackneyed topic, and I must therefore begin by craving your indulgence. I was moved to make it the subject of this evening's lecture by the fact that I have lately been reading the book in which the most important of the late Professor Prichard's scattered writings on Sense-perception have been collected by Sir W. D. Ross. Like everything that Prichard wrote, these essays are extremely acute, transparently honest, and admirably thorough. I shall not attempt here either to expound or to criticize Prichard, but he may be taken to be hovering, perhaps somewhat disapprovingly, in the background during the lecture.