There is also a whole host of objections in the literature to Williams’ trope bundle theory. According to Williams, concrete particulars are not substrata instantiating various properties. They are wholly constructed out of tropes, forming bundles of tropes, the trope constituents of which are pairwise tied together by a compresence relation. Compresence, in turn, is collocation for Williams, “the unique congress in the same volume.” (In order to allow for non-spatial objects, Williams grants the possibility of “locations” in systems analogous to space (1966, 79).) One immediate worry, raised by Campbell, is the possibility that there may be cases of overlapping objects demonstrating that collocation is not sufficient for compresence (1990, footnote 5, 175). In response, the trope bundle theorist can opt for the view that compresence is non-reducible. However, even with this revision there remain significant objections concerning the possibility of accidental properties, the possibility of change, and an apparent vicious regress of compresence relations.