Any attempt to divide the world into portions, of which one is more “real” than the other, is doomed to failure.
 Bertrand Russell, A History of Western Philosophy (1945). copy citation

Context

“Plato would not dream of denying that there appear to be many beds, although there is only one real bed, namely the one made by God. But he does not seem to have faced the implications of the fact that there are many appearances, and that this many-ness is part of reality. Any attempt to divide the world into portions, of which one is more “real” than the other, is doomed to failure. Connected with this is another curious view of Plato’s, that knowledge and opinion must be concerned with different subject-matters. We should say: If I think it is going to snow, that is opinion; if later I see it snowing, that is knowledge;” source