  Why, though, should we suppose that this necessitation thesis (that if one trope is fully constituted by another trope, then it necessarily is) is true?  Robb’s own thesis was actually about trope identity rather than trope constitution, and this gives Robb’s thesis more immediate plausibility, as identity does seem to be necessary. Shafer-Landau, however, wants to appeal to constitution rather than identity (this is a departure from Robb), and this makes it very unclear why we should accept the analogous necessitation thesis.