80. Scientific Systematization. There are three factors of this (tres modi sciendi -- three modes of knowing): definition; demonstration; division.

Definition furnishes the principles; demonstration passes from principles to conclusions. While the definition says what a thing is, it shows in what that thing differs from things of another species comprised in the same genus. Thus differentiation, or division, is the auxiliary of definition.

Having studied the function of definition and division, and the conditions under which they are employed (§ 1) (demonstration has already been sufficiently treated) we shall enquire how these factors adapt themselves to the various sciences and to philosophy: the study of method in general and of the methods respectively appropriate to the various groups of sciences (§ 2).