LXXXV.
We take for granted that each kind of things has a special character which may be expressed by a Definition. The ground of our assumption is this;—that reasoning must be possible. (viii. 1.)
LXXXVI.
The “Five Words,” Genus, Species, Difference, Property, Accident, were used by the Aristotelians, in order to express the subordination of Kinds, and to describe the nature of Definitions and Propositions. In modern times, these technical expressions have been more referred to by Natural Historians than by Metaphysicians. (viii. 1.)
LXXXVII.
The construction of a Classificatory Science includes Terminology, the formation of a descriptive language;—Diataxis, the Plan of the System of Classification, called 21 also the Systematick;—Diagnosis, the Scheme of the Characters by which the different Classes are known, called also the Characteristick. Physiography is the knowledge which the System is employed to convey. Diataxis includes Nomenclature. (viii. 2.)
LXXXVIII.
Terminology must be conventional, precise, constant; copious in words, and minute in distinctions, according to the needs of the science. The student must understand the terms, directly according to the convention, not through the medium of explanation or comparison. (viii. 2.)
LXXXIX.
The Diataxis, or Plan of the System, may aim at a Natural or at an Artificial System. But no classes can be absolutely artificial, for if they were, no assertions could be made concerning them. (viii. 2.)