Accordingly we must first take the genus, in which are the points that are nearest those above; and after this the next difference. And the succession of differences, when cut and divided, completes the "What it is." There is no necessity for expressing all the differences of each thing, but those which form the species.
Geometrical analysis and synthesis are similar to logical division and definition; and by division we get back to what is simple and more elementary. We divide, therefore, the genus of what is proposed for consideration into the species contained in it; as, in the case of man, we divide animal, which is the genus, into the species that appear in it, the mortal, and the immortal. And thus, by continually dividing those genera that seem to be compound into the simpler species, we arrive at the point which is the subject of investigation, and which is incapable of further division.
For, after dividing "the animal" into mortal and immortal, then into terrestrial and aquatic; and the terrestrial again into those who fly and those who walk; and so dividing the species which is nearest to what is sought, which also contains what is sought, we arrive by division at the simplest species, which contains nothing else, but what is sought alone.
For again we divide that which walks into rational and irrational; and then selecting from the species, apprehended by division, those next to man, and combining them into one formula, we state the definition of a man, who is an animal, mortal, terrestrial, walking, rational.
Whence Division furnishes the class of matter, seeking for the definition the simplicity of the name; and the definition of the artisan and maker, by composition and construction, presents the knowledge of the thing as it is; not of those things of which we have general notions. To these notions we say that explanatory expressions belong. For to these notions, also, divisions are applicable.
Now one Division divides that which is divided into species, as a genus; and another into parts, as a whole; and another into accidents.
The division, then, of a whole into the parts, is, for the
