Reading John Anderson has enhanced my sense of the centrality of the question of levels of reality for those of us who view philosophy as a quest for the Absolute and a project of self-transformation. Of course it was more or less obvious to me all along, Plato's Allegory of the Cave being the richest depiction we have of the two-world theme.
Essential to religion is the belief that there is what William James calls an "unseen order" (Varieties of Religious Experience, 53), a higher order, above or behind the phenomenal order of time and change, doubt and confusion, mendacity and evil.
The unseen order is to be affirmed without the phenomenal order being denied. So there are two levels of reality. How exactly they are related is the problem, or one problem. We will pursue the problem in due course in connection with John Passmore's discussion of the "Two-Worlds Argument" in his Philosophical Reasoning.