 Remarkably, not only are black holes in and of themselves objects of the utmost simplicity. They enforce simplicity on all else in the universe as well, no matter how far away from themselves. In a sense that can be made precise, one of the most basic structures of the spacetime manifold itself, its topology, is as simple as possible everywhere outside a well behaved black  hole.[10]  This is known as the Topological Censorship Theorem (Friedman et al. 1983; Chruściel and Wald 1994; Galloway 1995). As its name suggests, it bears on the larger question of the Cosmic Censorship Hypothesis (Galloway and Woolgar 1997), discussed in  section 4  below. In itself, though, it raises fascinating questions about the relation of topological to metrical structure in a spacetime, questions almost completely unexplored by philosophers. (See Geroch and Horowitz 1979 for a long list of conceptual and technical problems and questions about this relation.) For a philosopher interested in the nature of spacetime, however, the way that its different structures relate to and constrain each other must be of fundamental importance. 