 Linsky and Zalta’s view entails that concreteness is an accidental property, in the sense that the self-same individual that is in fact nonconcrete (my possible brother, for example) could have been concrete and the self-same individual that is in fact concrete (both you and me, for example) could have been nonconcrete. Many metaphysicians will reject this on the grounds that concreteness is categorical and an individual does not migrate through categorical properties across modal space. But now consider the temporal analog of the modal issues with existence and concreteness that we have been exploring: The problem of temporary existents. While one’s accounts of the two problems do not need to swing together (Linsky and Zalta, for example, do not offer the temporal analog of their account of contingent existents), as there are differences between alethic modality and temporality, it is useful to consider them as a pair for our purposes.  Intuitively things come in and go out of existence; what exists at one time does not exist at another. The temporal analog of Linsky and Zalta’s view of contingent existents entails that everything always exists. What there is and what exists at one time is the same as what is and what exists at any other time; the domain of quantification is fixed across all times. What varies from time to time is instead which of those individuals are concrete. Socrates still exists now, although as a nonconcrete individual, who was concrete in 450 BCE, and similarly for the first child to be born in 2150. This view requires that a thing can survive the change from being nonconcrete to concrete, which is the explanation of what the ancients would call generation, and the change from being concrete to nonconcrete, which is the explanation of what the ancients would call destruction. On this view, then, seeming substantial changes are really forms of qualitative change: A change in the quality of concreteness. This runs contrary to the common conception that concreteness is necessary and eternal to any object that instantiates it, the divide between concrete and nonconcrete individuals marking a divide between categories of being. Many metaphysicians insist that, just as one and the same thing cannot go from being an individual to being a property, so too one and the same thing cannot go from being nonconcrete to being concrete.