ABSTRACT
Intuitively extensions can be thought of as the extents which certain kinds of terms range over and intensions as that in virtue of which they do so. Extensions correspond roughly to classes, and intensions to properties. A property like that of being a man determines at most one class. There is only one class of men, though it may have subclasses. But one and the same class may correspond to more than one property. The class of ruminants, for example, is the same as the class of cloven-hoofed animals. A class itself can be defined in extension or in intension; see UNIVERSALS.
