UNCOMPLEMENTED CATEGORIES, OR, WHAT IS IT LIKE TO BE A BACHELOR?

To learn and to use a category one must be able to sample both what is in it and what is not in it (i.e., what is in its complement), in order to pick out which invariant features distinguish members from nonmembers. Categories without complements may be responsible for certain conceptual and philosophical problems. Examples are experiential categories such as what it feels like to "be awake," "be alive," be aware," and "be." Providing a complement by analogy or extrapolation is a solution in some cases (such as what it feels like to be a bachelor), but only because the complement can in princible be sampled in the future, and because the analogy could in principle be correct. Where the complement is empty in principle, the "category" is intrinsically problematic. Other examples may include self-denial paradoxes (such as "this sentence is false") and problems with the predicate "exists."