Discussions of supervenience often appeal to property sets that are closed under such operations. But this is not a trivial assumption, for two reasons. First, it is controversial whether complementation, conjunction, and disjunction are legitimate property-forming operations. Whether they are largely depends upon what properties are taken to be. If properties are just the semantic values of predicates, then there are negative, conjunctive, and disjunctive properties, because negative, conjuncti