 Meinongianism is the thesis that there are objects that do not exist and so included in the most unrestricted domain of quantification and discourse are nonexistent entities. One immediate challenge for the Meinongian is to offer individuating conditions for nonexistents. The most straightforward comprehension principle is the naive principle that, for any condition on objects, there is a unique object satisfying exactly that condition. For our purposes, we can conceive of a condition as determining a set of properties; crudely, the properties expressed by the predicates composing the condition. In that case, condition C is the same condition as C′ when they determine the same set of properties. It follows that corresponding to any set of properties, there is exactly one object with exactly those properties. The naive comprehension principle faces several problems. In what remains of this section, we shall present these problems and distinguish different versions of Meinongianism in terms of the devices employed to develop a restricted comprehension principle for objects that avoids those problems. (All of these problems are developed in Russell’s discussion of Meinong, see [Russell 1905a, 1907]. For a discussion of the debate between Russell and Meinong, see [Smith 1985].)