Since what makes a thing that which it is, by the same fact differentiates this thing from every other thing, the essence is rightly conceived as that which gives the thing its characteristic being, thereby marking it off from all other being. In reality, of course, each individual being is distinct by all that it is from every other. But since we get our intellectual knowledge of things by abstracting, comparing, generalizing, and classifying partial aspects of them, we apprehend part of the imperfectly grasped abstract essence of each individual as common to other classes (generic), and part as peculiar to that class itself (differential); and thus we differentiate classes of things by what is only part of their essence, by what we call the differentia of each class, distinguishing mentally between it and the generic element: which two are really one, really identical, in every individual of the species thus defined and classified.
But in the Aristotelian and scholastic view of the constitution of any corporeal thing, there is a danger of taking what is really only part of the essence of such a thing for the whole essence. According to this view all corporeal substance is essentially composite, constituted by two really distinct, substantial principles, primal matter (πρώτη ὕλη, materia prima) and substantial form (ἔιδος, μορφή) united substantially, as potential and actual principles, to form one composite nature or essence. Now the kind, or species, or specific type, to which a body belongs—e.g., a horse, an oak, gold, water, etc.—depends upon the substantial form which [pg 078] actualizes the matter or potential principle. In so far as the corporeal essence is known to us at all it is known through the form, which is the principle of all the characteristic properties and activities of that particular kind of body. Hence it is quite natural that the εἲδος, μόρφη, or forma substantialis of a body should often be referred to as the specific essence of the body, though of course the essence of the body really includes the material as well as the formal factor.
We may look at the essence of any being from two points of view. If we consider it as it is conceived actually to exist in the being, we call it the physical essence. If we consider it after the manner in which it is apprehended and defined by our intellects through generic and differentiating concepts, we call it the metaphysical essence. Thus, the essence of man conceived by the two defining concepts, “rational animal,” is the metaphysical essence; the essence of man as known to be composed of the two really distinct substantial principles, soul and body, is the physical essence. Understood in this way both are one and the same essence considered from different points of view—as existing in the actual order, and as conceived by the mind.[87]
The physical essence of any being, understood as the constitutive principle or principles from which all properties spring, is either simple or composite according as it is understood to consist of one such constitutive principle, or to result from the substantial union of two constitutive principles, a material and a formal. Thus, the essence of God, the essence of a purely spiritual being, the essence of the human soul, are physically simple; the essence of man, the essences of all corporeal beings, are physically composite.
According to our mode of conceiving, defining and classifying essences by means of the abstract generic and differential grades of being which we apprehend in them, all essences, even physically simple essences, are conceived as logically and metaphysically composite. Moreover we speak and think of their generic and differential [pg 079] factors as “material” and “formal” respectively, after the analogy of the composition of corporeal or physically composite essences from the union of two really distinct principles, matter and form; the analogy consisting in this, that as matter is the indeterminate principle which is determined and actuated by form, so the generic concept is the indeterminate concept which is made definite and specific by that of the differentia.[88] But when we think of the genus of any corporeal essence as “material,” and the differentia as “formal,” we must not consider these “metaphysical parts” as really distinct; whereas the “physical parts” of a corporeal substance (such as man) are really distinct. The genus (animal), although a metaphysical part, expresses the whole essence (man) in an indeterminate way; whereas the “matter” which is a physical part, does not express the whole essence of man, nor does the soul which is also a physical part, but only both together. Not a little error has resulted from the confusion of thought whereby genus and differentia have been regarded as material and formal constitutives in the literal sense of those expressions.
14. Characteristics of Abstract Essences.—When we consider the essences of things not as actually existing, but as intrinsically possible—the abstract, metaphysical essences, therefore—we find that when as objects of our thought they are analysed into their simplest constituents and compared or related with themselves and with one another they present themselves to our minds in these relations as endowed with certain more or less remarkable characteristics.
(a) In the first place, being abstract, they present themselves [pg 080] to the mind as being what they are independently of actual existence at any particular time or place. Their intelligibility is something apart from any relation to any actual time or place. Being intrinsically possible, they might exist at any time or place; but as possible, they are out of time and out of place—detemporalized and delocalized, if we may be permitted to use such expressions.[89]
(b) Furthermore, since the intellect forms its notions of them, through the aid of the senses and the imagination, from actual realizations of themselves or their constituent factors, and since it understands them to be intrinsically possible, or free from intrinsic incompatibility of their constituent factors, it conceives them to be capable of indefinitely repeated actualizations throughout time and space—unless it sees some special reason to the contrary, as it does in the case of the Necessary Being, and (according to some philosophers) in the case of purely immaterial beings or pure spirits. That is to say it universalizes them, and sees them to be capable of existing at any and every conceivable time and place. This relation of theirs to space is not likely to be confounded with the immensity or ubiquity of God. But their corresponding relation to time is sometimes described as eternity; and if it is so described it must be carefully distinguished from the positive eternity of God, the Immutable Being. To distinguish it from the latter it is usually described as negative eternity,—this indifference of the possible essence to actual existence at any particular point of time.
But apart from this relation which we conceive it as having to existence in the order of actual reality, can we, or do we, or must we conceive it as in itself an intrinsic possibility from all eternity, in the sense that it never began to be intrinsically possible, and will never cease to be so? Must we attribute to it a positive eternity, not of course of actuality or existence, but of ideal being, as an object of thought to an Eternally Existing Mind? What is this supposed eternal possibility of the possible essence? Is it nothing actual: the possible as such is nothing actual. But is it anything real? Has it only ideal being—esse ideale or intentionale? And has it this only in and from the human mind, or independently of the human mind? And also independently of the actual essences from which the human mind gets the data for its thought,—so that we must ascribe to it an eternal ideal being? To these questions we shall return presently.
(c) Thirdly, essences considered apart from their actual existence, and compared with their own constitutive factors or with one another, reveal to the mind relations which the mind sees to [pg 081] be necessary, and which it formulates for itself in necessary judgments,—judgments in materia necessaria. By virtue of the principle of identity an abstract essence is necessarily what it is, what the mind conceives it to be, what the mind conceives as its definition. Man, as an object of thought, is necessarily a rational animal, whether he actually exists or not. And if he is thought of as existing, he cannot at the same time be thought of as non-existing,—by the principle of contradiction. An existing man is necessarily an existing man,—by the principle of identity. These logical principles are rooted in the nature of reality, whether actual or possible, considered as an object of thought. There is thus a necessary relation between any complex object of thought and each of the constituent factors into which the mind can analyse it. And, similarly, there is a necessary negative relation—a relation of exclusion—between any object of thought and anything which the mind sees to be incompatible with that object as a whole, or with any of its constituent factors.