 The distinction between nuclear and extra-nuclear properties remains unclear. Parsons introduced the distinction with lists of nuclear predicates (‘is blue’, ‘is tall’, ‘kicked Socrates’, ‘is a mountain’) and extra-nuclear predicates (‘exists’, ‘is thought about by Meinong’, ‘is complete’). He then tells us that the extra-nuclear are those that do not stand for properties of individuals ([Parsons 1980, 24]). And, of course, it is nuclear and not extra-nuclear properties by which objects are individuated. Parsons’s individuation principle for objects is the following: “(1) No two objects (real or unreal) have exactly the same nuclear properties; and (2) For any set of nuclear properties, some object has all the properties in that set and no other nuclear properties” ([Parsons 1980, 19]). But it is not clear what status individual identity properties—properties like being identical to A, where A is an individual substance like, say, Parsons himself—have with respect to this distinction. He sometimes claims that they are extra-nuclear properties ([Parsons 1980, 28]). In that case, however, Parsons is committed to the problematic thesis of the identity of indiscernibles and so the impossibility of two primitively distinct but qualitatively identical objects. (For further discussion, see the entry on  the identity of indiscernibles.) Many contemporary philosophers agree that objects are not individuated qualitatively, their identity and diversity being primitive. Max Black’s two qualitatively indiscernible spheres are primitively distinct, in virtue of which one has the property of being that very thing and the other lacking that property (see [Black 1953]). For Parsons to accept this, he needs to include individual identity properties among the nuclear properties. Furthermore, it is hard to see why identity properties are not properties of individuals. Suppose, then, that we count individual identity properties like being identical to A as nuclear properties, those properties entering the range of Parsons’s restricted comprehension principle. Then the nuclear negations of those properties are also nuclear. But then we can take the set of all objects, construct the individual identity property for each, construct the nuclear negation of each of those properties, and then construct a condition from those properties that, by Parsons’s comprehension principle, corresponds to an object.  Then there is an object that is distinct from every object that there is, which is a contradiction. It is unclear, then, that the distinction between nuclear and extra-nuclear properties and the restriction of the comprehension principle to nuclear properties solves the problems facing the naive comprehension principle. (For further discussion of Parsons’s view, see [Fine 1982, 1984] and [Zalta 1992].)