For the comprehension of analysis, it is necessary to investigate the notion of whole and part, a notion which has been wrapped in obscurity—though not without certain more or less valid logical reasons—by the writers who may be roughly called Hegelian. In the present chapter I shall do my best to set forth a straightforward and non-mystical theory of the subject, leaving controversy as far as possible on one side. It may be well to point out, to begin with, that I shall use the word whole as strictly correlative to part, so that nothing will be called a whole unless it has parts. Simple terms, such as points, instants, colours, or the fundamental concepts of logic, will not be called wholes.(§ 133 ¶ 1)

Terms which are not classes may be, as we saw in the preceding chapter, of two kinds. The first kind are simple: these may be characterized, though not defined, by the fact that the propositions asserting the being of such terms have no presuppositions. The second kind of terms that are not classes, on the other hand, are complex, and in their case, their being presupposes the being of certain other terms. Whatever is not a class is called a unit, and thus units are either simple or complex. A complex unit is a whole; its parts are other units, whether simple or complex, which are presupposed in it. This suggests the possibility of defining whole and part by means of logical priority, a suggestion which, though it must be ultimately rejected, it will be necessary to examine at length.(§ 133 ¶ 2)