[7] Aristot. Categor. p. 1, a. 1-15.
We can hardly doubt that it was Aristotle who first gave this peculiar distinctive meaning to the two words Homonymous and Synonymous, rendered in modern phraseology (through the Latin) Equivocal and Univocal. Before his time this important distinction between different terms had no technical name to designate it. The service rendered to Logic by introducing such a technical term, and by calling attention to the lax mode of speaking which it indicated, was great. In every branch of his writings Aristotle perpetually reverts to it, applying it to new cases, and especially to those familiar universal words uttered most freely and frequently, under the common persuasion that their meaning is not only thoroughly known but constant and uniform. As a general fact, students are now well acquainted with this source of error, though the stream of particular errors flowing from it is still abundant, ever renewed and diversified. But in the time of Aristotle the source itself had never yet been pointed out emphatically to notice, nor signalized by any characteristic term as by a beacon. The natural bias which leads us to suppose that one term always carries one and the same meaning, was not counteracted by any systematic warning or generalized expression. Sokrates and Plato did indeed expose many particular examples of undefined and equivocal phraseology. No part of the Platonic writings is more valuable than the dialogues in which this operation is performed, forcing the respondent to feel how imperfectly he understands the phrases constantly in use. But it is rarely Plato’s practice to furnish generalized positive warnings or systematic distinctions. He has no general term corresponding to homonymous or equivocal; and there are even passages where (under the name of Prodikus) he derides or disparages a careful distinctive analysis of different significations of the same name. To recognize a class of equivocal terms and assign thereto a special class-name, was an important step in logical procedure; and that step, among so many others, was made by Aristotle.[8]
[8] In the instructive commentary of Dexippus on the Categoriæ (contained in a supposed dialogue between Dexippus and his pupil Seleukus, of which all that remains has been recently published by Spengel, Munich, 1859), that commentator defends Aristotle against some critics who wondered why he began with these Ante-predicaments (ὁμώνυμα, συνώνυμα, &c.), instead of proceeding at once to the Predicaments or Categories themselves. Dexippus remarks that without understanding this distinction between equivoca and univoca, the Categories themselves could not be properly appreciated; for Ens — τὸ ὂν — is homonymous in reference to all the Categories, and not a Summum Genus, comprehending the Categories as distinct species under it; while each Category is a Genus in reference to its particulars. Moreover, Dexippus observes that this distinction of homonyms and synonyms was altogether unknown and never self-suggested to the ordinary mind (ὅσων γὰρ ἔννοιαν οὐκ ἔχομεν, τούτων πρόληψιν οὐκ ἔχομεν, p. 20), and therefore required to be brought out first of all at the beginning; whereas the Post-predicaments (to which we shall come later on) were postponed to the end, because they were cases of familiar terms loosely employed. (See Spengel, Dexipp. pp. 19, 20, 21.)
Though Aristotle has professed to distinguish between terms implicated in predication, and terms not so implicated,[9] yet when he comes to explain the functions of the latter class, he considers them in reference to their functions as constituent members of propositions. He immediately begins by distinguishing four sorts of matters (Entia): That which is affirmable of a Subject, but is not in a Subject; That which is in a Subject, but is not affirmable of a Subject; That which is both in a Subject, and affirmable of a Subject; That which is neither in a Subject, nor affirmable of a Subject.[10]
[9] Aristot. Categor. p. 1, a. 16. τῶν λεγομένων τὰ μὲν κατὰ συμπλοκὴν λέγεται, τὰ δ’ ἄνευ συμπλοκῆς· τὰ μὲν οὖν κατὰ συμπλοκὴν οἷον ἄνθρωπος τρέχει, ἄνθρωπος νικᾷ· τὰ δ’ ἄνευ συμπλοκῆς οἶον ἄνθρωπος, βοῦς, τρέχει, νικᾷ.
It will be seen that the meaning and function of the single word can only explained relatively to the complete proposition, which must be assumed as foreknown.
That which Aristotle discriminates in this treatise, in the phrases — λέγεσθαι κατὰ συμπλοκὴν and λέγεσθαι ἄνευ συμπλοκῆς is equivalent to what we read in the De Interpretatione (p. 16, b. 27, p. 17, a. 17) differently expressed, φωνὴ σημαντικὴ ὡς κατάφασις and φωνὴ σημαντικὴ ὡς φάσις.
[10] Aristot. Categor. p. 1, a. 20.
This fundamental quadruple distinction of Entia, which serves as an introduction to the ten Categories or Predicaments, belongs to words altogether according to their relative places or functions in the proposition; the meanings of the words being classified accordingly. That the learner may understand it, he ought properly to be master of the first part of the treatise De Interpretatione, wherein the constituent elements of a proposition are explained: so intimate is the connection between that treatise and this.
The classification applies to Entia (Things or Matters) universally, and is thus a first step in Ontology. He here looks at Ontology in one of its several diverse aspects — as it enters into predication, and furnishes the material for Subjects and Predicates, the constituent members of a proposition.