 This article is largely a historical survey of prominent views. However, it is hard to fully understand those debates without knowing something about scientific and mathematical developments have changed recent understanding of the issues. In particular, a spacetime approach can clarify the situation with which the interlocutors were wrestling, and help clarify their arguments. This is a point widely recognized in the secondary literature, and indeed colors much of what is said there (for good and bad, as we shall touch on later). So a short digression into these matters is important for engaging the literature responsibly; that said, while §7 presupposes this section, the reader only interested in §6 could skip this section.