 Temporal parts theory may suggest another line of defense. William Vallicella says briefly that an occasionalist can affirm the persistence of created things by holding that time is continuous and that persisting objects are composed of continuum-many temporal parts (Vallicella 1996, 353 n. 20). If this is correct, then a continuous creation theorist can presumably do the same. David Vander Laan considers a temporal-parts strategy and finds it problematic. Given a sufficiently inclusive theory of composition, he argues, a series of objects may indeed compose an object that exists at various times and thereby persists, but if there are no causal relations between these objects it does not seem that their sum could be, e.g., a human person. Arbitrary cross-temporal sums need not be united by internal causal relations, but persons must (Vander Laan 2006, 164).