Let us now look at Plato’s argument, and his definition of existence, as they bear upon the doctrine of the opposing Materialist philosophers, whom he states to have held that bodies alone existed, and that the Incorporeal did not exist:— in other words that all real existence was concrete and particular: that the abstract (universals, forms, attributes) had no real existence, certainly no separate existence. As I before remarked, it is not quite clear what or how much these philosophers denied. But as far as we can gather from Plato’s language, what they denied was, the existence of attributes apart from a substance. They did not deny the existence of just and wise men, but the existence of justice and wisdom, apart from men real or supposable.
Difference between Concrete and Abstract, not then made conspicuous. Large meaning here given by Plato to Ens — comprehending not only objects of Perception, but objects of Conception besides.
In the time of Plato, distinction between the two classes of words, Concrete and Abstract, had not become so clearly matter of reflection as to be noted by two appropriate terms: in fact, logical terminology was yet in its first rudiments. It is therefore the less matter of wonder that Plato should not here advert to the relation between the two, or to the different sense in which existence might properly be predicable of both. He agrees with the materialists or friends of the Concrete, in affirming that sensible objects, Man, Horse, Tree, exist (which the Idealists or friends of the Abstract denied): but he differs from them by saying that other Objects, super-sensible and merely intelligible, exist also — namely, Justice, Virtue, Whiteness, Hardness, and other Forms or Attributes. He admits that these last-mentioned objects do not make themselves manifest to the senses; but they do make themselves manifest to the intelligence or the conception: and that is sufficient, in his opinion, to authenticate them as existent. The word existent, according to his definition (as given in this dialogue), includes not only all that is or may be perceived, but also all that is or may be known by the mind; i.e., understood, conceived, imagined, talked or reasoned about. Existent, or Ens, is thus made purely relative: having its root in a Subject, but ramifying by its branches in every direction. It bears the widest possible sense, co-extensive with Object universally, either of perception or conception. It includes all fictions, as well as all (commonly called) realities. The conceivable and the existent become equivalent.
Narrower meaning given by Materialists to Ens — they included only Objects of Perception. Their reasoning as opposed to Plato.
Now the friends of the Concrete, against whom Plato reasons, used the word existent in a narrower sense, as comprising only the concretes of the sensible world. They probably admitted the existence of the abstract, along with and particularised in the concrete: but they certainly denied the separate existence of the Abstract — i.e., of Forms, Attributes, or classes, apart from particulars. They would not deny that many things were conceivable, more or less dissimilar from the realities of the sensible world: but they did not admit that all those conceivable things ought to be termed existent or realities, and put upon the same footing as the sensible world. They used the word existent to distinguish between Men, Horses, Trees, on the one hand — and Cyclopes, Centaurs, Τραγέλαφοι, &c., on the other. A Centaur is just as intelligible and conceivable as either a man or a horse; and according to this definition of Plato, would be as much entitled to be called really existent. The attributes of man and horse are real, because the objects themselves are real and perceivable: the class man and the class horse is real, for the same reason: but the attributes of a Centaur, and the class Centaurs, are not real, because no individuals possessing the attributes, or belonging to the class, have ever been perceived, or authenticated by induction. Plato’s Materialist opponents would here have urged, that if he used the word existent or Ens in so wide a sense, comprehending all that is conceivable or nameable, fiction as well as reality — they would require some other words to distinguish fiction from reality — Centaur from Man: which is what most men mean when they speak of one thing as non-existent, another thing as existent. At any rate, here is an equivocal sense of the word Ens — a wider and a narrower sense — which, we shall find frequently perplexing us in the ancient metaphysics; and which, when sifted, will often prove, that what appears to be a difference of doctrine, is in reality little more than a difference of phraseology.[110]
[110] Plato here aspires to deliver one definition of Ens, applying to all cases. The contrast between him and Aristotle is shown in the more cautious procedure of the latter, who entirely renounces the possibility of giving any one definition fitting all cases. Aristotle declares Ens to be an equivocal word (ὁμώνυμον), and discriminates several different significations which it bears: all these significations having nevertheless an analogical affinity, more or less remote, with each other. See Aristot. Metaphys. Δ. 1017, a. 7, seq.; vi. 1028, a. 10.
It is declared by Aristotle to be the question first and most disputed in Philosophia Prima, Quid est Ens? καὶ δὴ καὶ τὸ πάλαι τε καὶ νῦν καὶ ἀεὶ ζητούμενον καὶ ἀεὶ ἀπορούμενον, τοῦτο ἐστι, τίς ἡ οὐσία (p. 1028, b. 2). Compare, B. 1001, a. 6, 31.
This subject is well treated by Brentano, in his Dissertation Ueber die Bedeutung des Seienden im Aristoteles. See pp. 49-50 seq., of that work.
Aristotle observes truly, that these most general terms are the most convenient hiding-places for equivocal meaning (Anal. Post. ii. 97, b. 29).
The analogical varieties of Ens or Essence are graduated, according to Aristotle: Complete, Proper, typical, οὐσία, stands at the head: there are then other varieties more or less approaching to this proper type: some of them which μικρὸν ἢ οὐθὲν ἔχει τοῦ ὄντος. (Metaphys. vi. 1029, b. 9.)