The relative merits of standard mereology have received quite a bit of attention in recent years from metaphysicians concerned with the part/whole properties of material objects. A question that has not been pursued to the same degree, however, is what sort of semantic repercussions a commitment to mereological sums in the standard sense might have in particular on the predicted behavior of singular terms and our practices of using such terms to refer to objects. The apparent mismatch between our actual referential practices and the persistence conditions attributed to material objects by the supporters of standard mereology puts these philosophers, other things being equal, at a disadvantage compared to those whose ontology matches more closely the observed behavior of singular terms, as they are commonly used in ordinary discourse. To alleviate this problem, David Lewis leans heavily on his distinction between natural and non-natural properties. I argue in this paper that Lewis’ already heavily burdened natural/non-natural distinction among properties is not enough to avoid Quinean indeterminacy for singular terms. Those who are in the business of giving an analysis of constructions involving full-fledged predication, as opposed to the mere spatial overlap of denotations, will thus want to go in for an ontology that places more stringent structural constraints on the referents of singular terms than would be supplied by standard mereology.