Negation as privation, in the January 21, 1965, Zollikon seminar.
[T]he state of rest is not a mere negation of motion but its privation, that is, it is a kind of motion. Otherwise, no new motion could ever originate from rest. The number 5, which cannot move, cannot also be something at rest.
It took Greek thinkers two hundred years to discover the idea of privation. Only Plato discovered this negation as privation and discussed it in his dialogue The Sophist. This happened in connection with the insight that not every instance of nonbeing simply means not existing but rather that there is nonbeing which, in a certain sense, is. The shadow is such a nonbeing in the sense of privation because it is a lack of brightness. Thus, not being healthy, being sick, is also a mode of existing in privation. The nature of being sick cannot be adequately grasped without a sufficient determination of being healthy. You will immediately see that we encounter this remarkable phenomenon of privation even more often in the context of the phenomenon of time. It is an ontological phenomenon, that is, it refers to a possibility of being and not merely to the logic of a propositional negation.
Shadows are my favorite nonbeings.