In the course of three paragraphs in her The Mind of the Maker, Dorothy Sayers manages to connect a number of these I’ve been thinking and posting about here recently: how sub-creation changes everything, the non-existence of non-existing possibles, and how non-being is not a correlate but the creation of Being:
What I want to suggest is that Being (simply by being) creates Not-Being… So that though, in the absence of Being, it would be meaningless to say that to say that Not-Being precedes Being; yet, in the presence of Being that proposition becomes both significant and true, because Being has made it so. Or, to use the most familiar of all metaphors, “before” light, there was neither light nor darkness; darkness is not darkness until light has made the concept of darkness possible. Darkness cannot say: “I precede the coming light,” but there is a sense in which light can say, “Darkness preceded me.”
Shakespeare writes Hamlet. That act of creation enriches the world with a new category of Being, namely: Hamlet. But simultaneously it enriches the world with a new category of Not-Being, namely: Not-Hamlet. Everything other than Hamlet, to the farthest bounds of the universe, acquires in addition to its former characteristics, the characteristic of being Not-Hamlet; the whole of the past immediately and automatically becomes Not-Hamlet.
Now, in a sense, it is true to say that the past was Not-Hamlet before Hamlet was created or thought-of; it is true, but it is meaningless, since apart from Hamlet there is no meaning that we can possibly attach to the term Not-Hamlet. Doubtless there is an event, X, in the future, by reference to which we may say that we are at present in a category of Not-X, but until X occurs, the category of Not-X is without reality. Only X can give reality to Not-X; that is to say, Not-Being depends for its reality upon Being. In this way we may faintly see how the creation of Time may be said automatically to create a time when Time was not, and how the Being of God can be said to create a Not-Being that is not God. (The Mind of the Maker 101)