ESSENCE. — I. It indicates the nature of a thing as such and therefore that which is signified in its definition. If the “being” (v.) is the subsistent concrete that exists or that possesses the act of being, e. is the special “nature” (ὁσία) that this act causes to exist. E. expresses in its content a “participation” in the infinite perfection of the divine nature; it determines for each being its proper place in the hierarchy of beings; it grounds, directs, and actualizes their respective possibilities of development. As an expression of the fundamental heterogeneity of reality, essences are fixed and immutable both in time and in space: they therefore succeed one another discontinuously, through intervals that are distinct degrees of perfection within the realm of being: such as lead, oak, horse, man... Aristotle accepted, with suitable corrections, the tradition of Platonic-Pythagorean intellectualism that “essences are in some way like numbers” (Met., IX, 3, 1043 b 32 ff.). Thus essences simultaneously ground the stability of being and the objectivity of knowing: hence the Neo-Latin term “quiddity” (quidditas = “quid sit aliquid”). E. is said both of substance and of accident, but of substance in the primary sense and of accident in a secondary sense and by analogy, since just as the accident, which is not so much “ens” as “ens entis,” shares in substance’s reason for being, so likewise its e. depends upon that of its own substance, so that in its definition the accident includes substance both as subject and foundation and as radical active principle (s. Thomas, In VII Met., lect. 4ª, n. 1334). God properly does not have e. but is the Pure Act of being, beyond every definition.
II. In its dual aspect, ontological and logical, e. admits of various degrees of consideration. First of all there is the singular and individual e., the humanity of Peter and Paul (the 268e vi). In Aristotelian realism this alone truly exists in reality, and it is therefore upon it that the further determinations of scientific consideration must be founded. Since in singular substances e. is found multiplied and individualized, Aristotle could not stop at “form” alone, as Plato did, but had to introduce matter as a co-principle of e.
Therefore sensible things have an e. composed of matter and form, the union of which gives the complete species: man, as such, is not soul alone, but the synthesis of soul and body (Met., VI, 1, 1025 b 31 ff., and VIII, 4–6, 1045 b 3 ff.). Singularity, however (the “humanity” as it is found in Peter, realized with “this” soul as the act of “this” body), cannot be an attribute of e. as such but must be referred to extra-essential principles (v. INDIVIDUATION, PRINCIPLE of).
On the strictly metaphysical plane, e. is properly defined as “form” (εἶδος) of being, and as such does not require the presence of matter: indeed, at the summit of the scale of beings stand the wholly immaterial “forms” (pure spirits). And in the sensible world itself e. is determined by form; man is this e. and not another by virtue of the spiritual soul that is his form; that the body too should have a special nature is in turn a requirement and an effect of this same soul, to which it is destined, since that which determines is act and not potency. Thus for Aristotle e., in its metaphysical absoluteness, is to be said to be “without matter” (Met., VIII, 7, 1032 b 14). The soul (forma partis) is the act of a composite e., the act of matter: “humanitas,” on the other hand, states the reality of the whole (forma totini), which embraces both matter and form in a synthesis that is a degree, mode, and form of being among the other forms expressed by the other essences (s. Thomas, In VI Met., lect. 9ª, n. 1460).
In the logical order e. definition (v.). Just as e. has real parts, matter and form, so definition has logical parts, which are genus and difference; from these results the species, which is the complete e. (Met., VIII, 9, 1034 b 20 ff.). It should be noted, however, that genus and difference are “formal parts” of the being, of which the one expresses the determinable element and the other the determining element, and only in this respect—that is, indirectly—do they correspond to the composition of matter and form. Among the Scholastics, those who, Avicèbron (v.), maintain a direct correspondence between the logical and ontological orders admit the composition of matter and form even in pure spirits. According to s. Thomas, on the other hand, intellectual substances are absolutely simple in the order of e., though not in the order of being, in which they are really composed of e. and act of being and therefore of substance and faculties, unlike God, who is simple in every respect (Sum. Theol., 1ª, q. 54, a. 1–3).
In the delicate Aristotelian terminology, τὸ τὸ ἄντιν must be distinguished from τὸ ἦν εἶναι, or τὸ ἀνθρώπῳ εἶναι: the former represents the generic content of e.; the latter indicates e. in its full and definitive determination. The dative has a possessive meaning; the imperfect (ἦν) is brachylogical: it indicates both the precedence of the concept over the concrete thing modeled upon it and the perennial character pertaining to essential being (Trendelenburg, Schwegler, Bonitz). In Aristotelian philosophy, which does not accept creation “ab aeterno,” such perenniality has a purely ideal meaning, because in fact the world had a beginning and every creature in it: and therefore every e., from the standpoint of existential duration, has the value corresponding to its own nature: finite duration in every respect if the nature is contingent (corruptible material essences), infinite duration (immortal essences) a parte post if the nature is spiritual (angels and human souls). V. ANIMA; FORMA.