  Objects can be either simple or complex. An object is simple  if it has no proper parts, and complex otherwise. Like  objects, universals too divide into simple and complex. A universal  is simple if it has no other universal as a constituent, and complex  otherwise. Complex universals accordingly come in two varieties:  conjunctive — the constituents of which are simply its  conjuncts — and structural. A structural universal U is  one that is exemplified by a complex object O, and its  constituents are universals (distinct from U) exemplified by  simple parts of O that are relevant to O's being an  instance of   U.[40]  It is important to note that, for Armstrong, the constituency  relation is not the mereological parthood relation. Rather, complex  universals (hence also complex facts of which they are constituents)  enjoy a “non-mereological mode of composition” (1997,  119–123) that, in particular, allows for a richer conception of their   structure.[41]  (An assumption of our simplified account here will be that both the  proper part of relation and the constituency relation are  well-founded. It follows that (i) there is no   gunk,  i.e., that every complex object is composed, ultimately, entirely of  simples and (ii) complex universals — hence the complex facts  in which they are exemplified — are ultimately  “grounded” in simple facts, i.e., that they cannot be  infinitely decomposed into further complex   universals/facts.[42])  