More subtly, the same noun may represent either (1) an attribute or action or else (2) an entity or condition having that attribute or engaging in that action. For instance, a thread has the attribute "length," but we may also refer to the object as "a length of thread." "Mass" may denote an attribute ("the mass of the planet") or an entity possessing that attribute ("a gigantic mass hurtling toward the sun"). Similar dual meanings may be observed for key terms in the study of human action, such as "life" and the various kinds of "value." Because our chief concern is philosophy rather than linguistics, we shall not attempt to identify all such alternative constructions here, but one should be aware of them to avoid confusion.

Occasionally, common language lacks a word to denote a valid concept. For example, what word in English would represent an individual in a herd of both male and female cattle? (Note that "cow" denotes only the female of the species.) Such gaps may give rise to a specialized technical vocabulary, such as biological nomenclature.