This little work contains the chief ideas gathered together for a course of lectures on the theory and history of aesthetics given at Harvard College from 1892 to 1895. The only originality I can claim is that which may result from the attempt to put together the scattered commonplaces of criticism into a system, under the inspiration of a naturalistic psychology. I have studied sincerity rather than novelty, and if any subject, as for instance the excellence of tragedy, is presented in a new light, the change consists only in the stricter application to a complex subject of the principles acknowledged to obtain in our simple judgments. My effort throughout has been to recall those fundamental aesthetic feelings the orderly extension of which yields sanity of judgment and distinction of taste.