In this chapter we shall examine the claim that presentism is incompatible with the special theory of relativity. We shall not so much be concerned with just how good it is as an argument against presentism, as merely to consider how it might impact on the world–time parallel. In discussions of this objection writers on both sides spend a lot of time setting out what they take the special theory of relativity to be. While this is important, it is in a sense subsidiary to our claim, which is not to take a stand on whether presentism is true or not, or even whether or not it is compatible with the special theory of relativity, but solely to investigate what a modal parallel would look like. We are not scientists, and are not making any claims about the physical structure of space and time. In fact we had better not be. The issue for semantics is not whether the special theory of relativity is correct or not, but rather what it is about the special theory of relativity which might contradict presentism, and how it might do so, and what an analogous modal example would look like. Some in the dispute seem to think it might be a contingent matter whether or not presentism is true (Crisp 2003, p. 215; Rea 2003, p. 248). At first sight this might seem an obvious disanalogy with actualism, since it hardly seems a contingent matter whether actualism is true.