Miscellanies 8.6.17

Before definitions, demonstrations, and divisions, one must first set out in how many ways the thing sought is spoken of; homonyms must be dealt with, and synonyms arranged distinctly according to their meanings. Then one must inquire whether the thing proposed is among those considered in relation to others or is taken by itself. After this: whether it is, what it is, what belongs to it incidentally; or also thus: whether it is, what it is, why it is. Toward the study of these, knowledge of particulars and of universals contributes, as do prior things and the divisions of them according to their differences. Induction, then, yields the universal and the definition; divisions yield the species, the essence, and the individual; the study of the number of meanings yields the grasp of the proper sense; and the working through of difficulties increases the differences in them and the demonstrations, and in general the study and what follows from it. From all of these, scientific knowledge and truth are established. Again, what is summed up from division becomes a definition; for the definition is taken both before division and after: before, when it is conceded or laid down; after, when it is demonstrated. And in perception the universal is summed up from the particular; for perception is the starting point of induction, and the universal is its end. Induction, then, does not show what a thing is, but that it is or is not; division presents what it is; and definition, like division, teaches the substance and what it is, but not whether it is; while demonstration makes clear all three: whether it is, what it is, and why it is. Some definitions also include the cause.