 Singular propositions are a combination of the abstract and concrete, which leads to problems. The modal problem arises because, on the one hand, there are reasons to think that all propositions, as abstract objects, exist necessarily, but, on the other hand, it is highly intuitive that ordinary individuals might not have existed and others could have existed, in which case the singular propositions containing them as constituents exist contingently. The solutions to this problem discussed above involve denying that there are singular propositions, denying that ordinary objects are contingent existents, or denying that propositions are necessary existents. The temporal problems we shall consider in this section arise because ordinary individuals change over time, including coming into and going out of existence. Propositions, on the other hand, are usually taken to be eternal objects — things that do not change over time and exist at all times.