These philosophers do not reflect that definition is impossible of eternal Essences (which the Platonic Ideas are), especially in cases where the objects are essentially unique, as Sun, or Moon, or Earth (p. 1040, a. 29). When they try to define Sun, they are forced to use phrases which are applicable to many in common; but Sun, (and each Idea) is particular and individual, like Kleon or Sokrates. Why does none of them produce a definition of an Idea? If any one tried, he would soon see the pertinence of the above remarks (b. 3). (Alexander, Bonitz, and Schwegler, all observe incidentally that the reasoning of what immediately precedes is weak and sophistical. Bonitz, p. 352, gives a good summary of the chapter, concluding: “Hoc capite non id ipsum demonstrat, res singulas non esse substantias, sed rerum singularum non esse definitionem neque scientiam; nimirum quum substantiæ vel unice vel potissimum esse definitionem demonstratum sit, c. 4, hoc si comprobat, illud simul est comprobatum.�)
It is farther evident that many apparent Essences are not strictly and truly Essences; for example, the parts of animals; since not one of them is separated from the whole (οὐθὲν γὰρ κεχωρισμένον αὐτῶν ἐστίν — p. 1040, b. 6; Alexander says ad loc.: οὐσίας ἐκεῖνά φαμεν ὅσα καθ’ αὑτὰ ὄντα δύναται τὸ οἰκεῖον ἔργον ἀποτελεῖν· οὐσία γὰρ οὐδὲν ἄλλο ἐστὶν ἢ τὸ ἀφ’ οὗ τὸ ἑκάστου ἔργον ἐκπληροῦται· οὐσία γὰρ καὶ εἶδος Σωκράτους ἡ τοῦ Σωκράτους ψυχή, ἀφ’ ἧς αὐτῷ τὸ τοῦ ἀνθρώπου ᾗ ἄνθρωπος ἔργον ἐκπληροῦν). When any one of them is separated, it exists only in the character of Matter — earth, fire, air; none of them, in this separate condition, being an unity, but only like a heap of grains of gold or tin before they are melted and combined into one. We might suppose, indeed, that the parts of the body, and the parts of the soul, of animated beings, come near to Essence, both one and the other, alike potentially and actually (b. 12), because they have principles of motion in their turnings (καμπαῖς), so that in some cases they continue separately alive after division. Still the functions of the part alone must be really regarded as nothing more than potential, wherever the oneness and continuity of the whole is the work of Nature (b. 15), and not a mere case of contact or forcible conjunction.
Nevertheless the being One, or Unity (p. 1040, b. 16), is not itself the Essence of things. Unum is predicated in the same manner as Ens; the two may always be predicated together: the Essence of Unum is One; and things of which the Essence is Unum Numero, are themselves numerically one. Neither Unum nor Ens is the Essence of things any more than the being an Element, or the being a Principle, can be the Essence thereof: we have farther to enquire what the Principle is, in order to bring the problem into a more cognizable shape (b. 20). Unum and Ens are more near to Essence than either Element, Principle, or Cause; nevertheless neither Unum nor Ens is Essence; for nothing which is common to many things is Essence. Essence belongs only to itself and to that which has itself. Farther, Unum cannot be in many places at once; but that which is common is in many places at once. It is thus plain that nothing Universal exists apart or separate from particulars (b. 27).
The advocates of the (Platonic) Ideas are right in affirming them to be separate, if they be Essences; but they are wrong in calling that which is predicable of many things (the Universal) an Idea (p. 1040, b. 29). When asked, What are these indestructible Essences of which you speak, as apart from the visible individual objects? — they had no intelligible answer to give. Accordingly they were forced to make these Essences the same specifically with the destructible (individual) objects; for these we do know (b. 33). They simply prefixed the word αὐτό to the names of sensible objects — αὐτοάνθρωπος, αὐτοΐππος. But these Ideas might still exist, even though we knew not what they were; just as eternal Essences like the stars would still exist, even though we had never seen them (p. 1041, a. 2).
Let us again examine what we call Essence, and what sort of thing it is; and let us take another point of departure, which may perhaps help us to understand what that Essence is which is apart and separate from perceivable Essences (p. 1041, a. 9). We know that Essence is a certain variety of Principle or Cause; and from this premiss we will reason (a. 10). Now the enquiry into Cause, or the Why, always comes in this shape: Why does one thing belong to another? The enquiry, Why a thing is itself? is idle. The fact — the ὅτι — must be assumed to be clear and known in the first instance. You know that the moon is eclipsed, as matter of fact; you proceed to enquire into the cause thereof (a. 11-24). Why does it thunder? or, to enunciate the same question more fully, Why is there noise in the clouds? The quæsitum is always one thing predicated of another (a. 26). Why are these materials, bricks and stones, a house? Here the answer sought is, the Cause; and that is the τ.η.ε., speaking in logical or analytical phraseology (λογικῶς — i.e., that which belongs to the λόγος τῆς οὐσίας). In some cases, this quæsitum is a Final Cause, as in the case of a bed or a house; in others, an Efficient or Movent Cause; for that also is a variety of Cause, generally sought for in regard to things generated or destroyed; but the other (viz., τὸ τ.η.ε., “ipsa rei forma ac notio, aut concepta in animo artificis, aut inclusa δυνάμει in ipsâ naturâ ac semine reiâ€� — Bonitz, Comm. p. 359) is sought for in regard to εἶναι.
The true nature of the quæsitum is often unperceived, when the problem is announced without stating distinctly the subject and predicate in their mutual relations (ἐν τοῖς μὴ καταλλήλως λεγομένοις, p. 1041, a. 33). For example, ἄνθρωπος διὰ τί ἐστιν; is ambiguous by imperfect enunciation. As it stands, it might be supposed to be intended as ἄνθρωπος διὰ τί ἐστιν ἄνθρωπος; which would be a question idle or null. To make it clear, you ought to distinguish the two members to which the real quæsitum refers (b. 2), and say διὰ τί τάδε ἢ τόδε ἐστὶν ἄνθρωπος; your real enquiry is about the ὕλη or Matter, why it exists in this or that manner. Why are these materials a house? Because the Essence of a house belongs to them (b. 6). Some τ.η.ε., some sort of εἶναι, must belong to the Matter (b. 4). Why is this Matter a man? or why is the body disposed in this particular way a man? Here we enquire as to the Cause which acts upon a certain Matter; and that is the Form whereby the thing is; which again is the Essence (b. 8).
Hence it is plain that a distinction must be taken between the Simple and the Compound. The enquiry above described, and the teaching above described, cannot apply to the Simple, which must be investigated in another way (p. 1041, b. 9). Compounds are of two sorts — aggregates like a heap (mechanical), and aggregates like a syllable (organic or formal). In these last there are not merely the constituent elements, but something else besides (b. 16). The syllable ba is something more than the letters b and a; flesh is something more than fire and earth, its constituent elements. Now this something more cannot be itself a constituent element; for, if that were so, flesh would be composed of three constituent elements instead of two, and we should still have to search for the something beyond, and this ulterior process might be repeated ad infinitum (b. 22). Nor can the something beyond be itself a compound of several elements, for we should still have to find the independent something which binds these into a compound. It is plain that this something beyond must be in its nature quite distinct from an element, and must be the cause why one compound is flesh, another compound a syllable, and so about all the remaining compounds. Now this is the Essence of each compound — the First Cause of existence to each (b. 25). The Element (στοιχεῖον) is that into which the compound is separated, as included Matter (ἐνυπάρχον ὡς ὕλην): b and a, in the syllable ba (b. 32). There are some things which are not the Essences of objects (white, for example, is not of the Essence of man, but an attribute); but, in all cases where compounds have come together according to Nature and by natural process, that Nature also which is not Element but Principle is the Essence (b. 28: ἐπεὶ δ’ ἔνια οὐκ οὐσίαι τῶν πραγμάτων, ἀλλ’ ὅσαι οὐσίαι κατὰ φύσιν καὶ φύσει συνεστήκασι, φανείη ἂν καὶ αὕτη ἡ φύσις οὐσία, ἥ ἐστιν οὐ στοιχεῖον ἀλλ’ ἀρχή. Schwegler in his note, p. 135, proposes to correct this passage by striking out καί before the words αὑτὴ ἡ φύσις οὐσία. But, if this were done, it would make the passage mean that ὕλη or στοιχεῖον is not οὐσία, and that the other φύσις which is not στοιχεῖον, is to be regarded exclusively as οὐσία. Now this is certainly not the doctrine of Aristotle, who expressly declares ὕλη to be οὐσία; see H, p. 1042, a. 32. Retaining the καί, the passage will then mean that not merely ὕλη, but also φύσις which is not ὕλη, is οὐσία).
Book Η.
In this Book, Aristotle begins by recapitulating the doctrines and discussions of the preceding. His purpose had been declared to be the investigation of the Causes, Principles, and Elements of Essences. Now Essences are diverse: some universally admitted, as the natural elements and simple bodies, also plants, animals, and the parts of each, lastly, the heaven and the parts thereof; others not universally admitted, but advocated by some philosophers, as the Ideas and Mathematical Entia; others, again, which we arrive at by dialectical discussion, as τὸ τ.η.ε., the Substratum (Logical Entia — ἐκ τῶν λόγων, p. 1042, a. 12), the Genus more Essence than the Species, the Universal more Essence than Particulars. The (Platonic) Ideas make a near approach to the Genus and the Universal; they are vindicated as Essences upon similar grounds. Next, since τὸ τ.η.ε. is Essence, and since the Definition is the rational explanation of τ.η.ε., we found it necessary to discuss Definition; and, since the Definition is a sentence having parts, we were called upon to examine these parts, and to explain what parts belonged both to Essence and to Definition. We decided farther, after discussion, that the Universal and the Genus were not Essence; the Platonic Ideas and the Mathematical Entia we postponed for the moment, and we confined ourselves to the perceivable Essences, recognized by all (a. 25).