his statement, “An existent in the observable world is either spatially coincident with something else or spatially separate from it,” referred to a single determination. On this basis, he then argued that this determination cannot be causally explained either by its being specifically a substance or by its being specifically an accident. We have shown, however, that it refers to two distinct determinations, causally explained by two distinct causes.

Fourth objection: We concede that this determination cannot be causally explained either by its being specifically a substance or by its being specifically an accident. Why, then, do you say that it must be causally explained either by temporal origination or by existence? What proves that these are the only possibilities? At most, one might say, “We have examined and investigated the matter and found no other category.” Yet we have explained in our more extensive works that failure to find something does not establish its nonexistence. We have also explained that this objection undermines every argument founded on open-ended classifications that are not confined to affirmation and negation.