So far, I have simply assumed that we live in a three-dimensional world that endures over time. But three-dimensionalism is not uncontested. Indeed, the greatest challenge to the Constitution View is four-dimensionalism. In this chapter, I first want to show that the challenges from four-dimensionalism do not unseat the intuitively satisfactory three-dimensionalism of ordinary life. I shall argue that three-dimensionalism is not ruled out by Theodore Sider's technical argument from vagueness for four-dimensionalism. Then, I shall show that, despite the fact that constitution is a vague relation, the Constitution View does not imply that the number of objects in ontology is indeterminate. Next, I shall argue that the so-called “paradoxes of coincidence” are no reason to favor four-dimensionalism over three-dimensionalism. I'll conclude with reasons to prefer three-dimensionalism over four-dimensionalism.

THREE – DIMENSIONALISM VS. FOUR – DIMENSIONALISM

Three–and four–dimensionalism differ with respect to whether or not objects have temporal parts in addition to their spatial parts. Four-dimensionalism is the view that “every object, x, has a temporal part at every moment, t, at which it exists.” A temporal part may be thought of as a temporal slice or a temporal segment of a physical object. Four-dimensionalism implies that if a baseball, say, exists from, say, t1 to t2, the baseball has a temporal part at every time in the interval between t1 and t2, and – here's the kicker – at each time t of its existence, it has a temporal part that exists at t and at no other time.