Identity and C hange. — The physical world contains both sameness and change. In perception, these two aspects are equally apparent. We recognize objects as essentially the same as they were years before. On the other hand, we can note slight differences intervening to mark the teeth of time. Familiar types of objects are, again, all around us, and their variety seems to have a limit in nature itself. Thus we are witnesses of repetition, novelty, persistence and change. The world is not a mere ﬂux, and yet it is not static and frozen. How can these aspects be combined?