Ontology, or the Science of Ens quatenus Ens, occupies an important place in Aristotle’s scientific programme; bearing usually the title of First Philosophy, sometimes Theology, though never (in his works) the more modern title of Metaphysica. He describes it as the universal and comprehensive Science, to which all other sciences are related as parts or fractions. Ontology deals with Ens in its widest sense, as an Unum not generic but analogical — distinguishing the derivative varieties into which it may be distributed, and setting out the attributes and accompaniments of Essentia universally; while other sciences, such as Geometry, Astronomy, &c., confine themselves to distinct branches of that whole;[11] each having its own separate class of Entia for special and exclusive study. This is the characteristic distinction of Ontology, as Aristotle conceives it; he does not set it in antithesis to Phenomenology, according to the distinction that has become current among modern metaphysicians.
[11] Aristot. Metaphys. Γ. p. 1003, a. 21, 25-33, E. p. 1025, b. 8. ἔστιν ἐπιστήμη τις ἢ θεωρεῖ τὸ ὂν ᾗ ὂν καὶ τὰ τούτῳ ὑπάρχοντα καθ’ αὑτό· αὕτη δ’ ἐστὶν οὐδεμιᾷ τῶν ἄλλων ἐπισκοπεῖ καθόλου περὶ τοῦ ὄντος ᾗ ὅν, ἀλλὰ μέρος αὐτοῦ τι ἀποτεμόμεναι περὶ τούτου θεωροῦσι τὸ συμβεβηκός, &c. Compare p. 1005, a. 2-14.
Now Ens (or Entia), in the doctrine of Aristotle, is not a synonymous or univocal word, but an homonymous or equivocal word; or, rather, it is something between the two, being equivocal, with a certain qualification. Though not a Summum Genus, i.e. not manifesting throughout all its particulars generic unity, nor divisible into species by the addition of well-marked essential differentiæ, it is an analogical aggregate, or a Summum Analogon, comprehending under it many subordinates which bear the same name from being all related in some way or other to a common root or fundamentum, the relationship being both diverse in kind and nearer or more distant in degree. The word Ens is thus homonymous, yet in a qualified sense. While it is not univocal, it is at the same time not absolutely equivocal. It is multivocal (if we may coin such a word), having many meanings held together by a multifarious and graduated relationship to one common fundamentum.[12] Ens (or Entia), in this widest sense, is the theme of Ontology or First Philosophy, and is looked at by Aristotle in four different principal aspects.[13]
[12] Simplikius speaks of these Analoga as τὸ μέσον τῶν τε συνωνύμων καὶ τῶν ὁμωνύμων, τὸ ἀφ’ ἑνός, &c. Schol. ad Categor. p. 69, b. 29, Brand. See also Metaphys. Z. p. 1030, a. 34.
Dexippus does not recognize, formally and under a distinct title, this intermediate stage between συνώνυμα and ὁμώνυμα. He states that Aristotle considered Ens as ὁμώνυμον, while other philosophers considered it as συνώνυμον (Dexippus, p. 26, book i. sect. 19, ed. Spengel). But he intimates that the ten general heads called Categories have a certain continuity and interdependence (συνέχειαν καὶ ἀλληλουχίαν) each with the others, branching out from οὐσία in ramifications more or less straggling (p. 48, book ii. sects. 1, 2, Spengel). The list (he says, p. 47) does not depend upon διαίρεσις (generic division), nor yet is it simple enumeration (ἀπαρίθμησις) of incoherent items. In the Physica, vii. 4, p. 249, a. 23, Aristotle observes: εἰσὶ δὲ τῶν ὁμωνυμιῶν αἱ μὲν πολὺ ἀπέχουσι αἱ δὲ ἔχουσαί τινα ὁμοιότητα, αἱ δ’ ἐγγὺς ἢ γένει ἢ ἀναλογίᾳ, διὸ οὐ δοκοῦσιν ὁμωνυμίαι εἶναι οὖσαι.
[13] Aristot. Metaphys. Δ. p. 1017, a. 7, E. p. 1025, a. 34, p. 1026, a. 33, b. 4; upon which last passage see the note of Bonitz.
1. Τὸ ὂν κατὰ συμβεβηκός — Ens per Accidens — Ens accidental, or rather concomitant, either as rare and exceptional attribute to a subject, or along with some other accident in the same common subject.
2. Τὸ ὂν ὡς ἀληθές, καὶ τὸ μὴ ὂν ὡς ψεῦδος — Ens, in the sense /of Truth, Non-Ens, in the sense of Falsehood. This is the Ens of the Proposition; a true affirmation or denial falls under Ens in this mode, when the mental conjunction of terms agrees with reality; a false affirmation or denial, where no such agreement exists, falls under Non-Ens.[14]
[14] Aristot. Metaph. E. 4, p. 1027, b. 18, — p. 1028, a. 4. οὐ γὰρ ἐστι τὸ ψεῦδος καὶ τὸ ἀληθὲς ἐν τοῖς πράγμασιν — ἀλλ’ ἐν διανοίᾳ — οὐκ ἔξω δηλοῦσιν οὖσάν τινα φύσιν τοῦ ὄντος. Also Θ. 10, p. 1051, b. 1: τὸ κυριώτατα ὂν ἀληθες καὶ ψεῦδος. In a Scholion, Alexander remarks: τὸ δὲ ὡς ἀληθῶς ὂν πάθος ἐστὶ καὶ βούλημα διανοίας, τὸ δὲ ζητεῖν τὸ ἑκάστῳ δοκοῦν οὐ σφόδρα ἀναγκαῖον.
3. Τὸ ὂν δυνάμει καὶ τὸ ὂν ἐνεργείᾳ — Ens, potential, actual.