 There is some residual unclarity in the notion of supervenience that figures in these theses. The idea is familiar enough—that there can be no relevant difference in objects in D without a relevant difference in their basic physical parts. I take it that the modality involved here is not logical but broadly physical. One might try to explicate the notion of supervenience here in terms of models of a true, descriptively complete, physical theory. At issue is whether such a physical theory has two models which agree on the qualitative intrinsic physical properties and relations of the basic parts of one or more objects in D but disagree on some qualitative intrinsic property or relation of these objects.