32. The “Principle of Individuation”.—How, then, are we to conceive this something which individuates reality? It may be well to point out that for the erroneous doctrine of extreme realism, which issues in monism, the problem of individuation, as here understood, does not arise. For the monist all plurality in being is merely apparent, not real: there can be no question of a real distinction between individual and individual.[145] Similarly, the nominalist and the conceptualist evade the problem. For these the individual alone is not merely formally real: it alone is fundamentally real: the universal is not even fundamentally real, has no foundation in reality, and thus all scientific knowledge of reality as revealed in sense experience is rendered [pg 126] impossible. But for the moderate realist, while the individual alone is formally real, the universal is fundamentally real, and hence the problem arises. It may be forcibly stated in the form of a paradox: That whereby Socrates and Plato are really distinct from each other as individuals is really identical with the human nature which is really in both. But what individuates human nature in Socrates, or in Plato, is logically distinct from the human nature that is really in Socrates, and really in Plato. We have only to inquire, therefore, whether the intrinsic principle of individuation is to be conceived merely as a negation, as something negative added by the mind to the concept of the specific nature, whereby the latter is apprehended as incapable of multiplication into “others” each of which would be formally that same nature, or, in other words, as incommunicable; or is the intrinsic ground of this incommunicability to be conceived as something positive, not indeed as something really distinct from, and superadded to, the specific nature, but as a positive aspect of the latter, an aspect, moreover, not involved in the concept of the specific nature considered in the abstract.
Of the many views that have been put forward on this question two or three call for some attention. In the opinion of Thomists generally, the principle which individuates material things, thus multiplying numerically the same specific nature, is to be conceived as a positive mode affecting the latter and revealing it in a new aspect, whereas the specific nature of the spiritual individual is itself formally an individual. The principle of the latter's individuation is already involved in the very concept of its specific nature, and therefore is not to be conceived as a distinct positive aspect of the latter but simply as the absence of plurality and communicability in the latter. In material things, moreover, the positive mode or aspect whereby the specific nature is found numerically multiplied, and incommunicable as it exists in each, consists in the fact that such a specific nature involves in its very constitution a material principle which is actually allied with certain quantitative dimensions. Hence the principle which individuates material substances is not to be conceived—after the manner in which Scotists conceive it—as an ultimate differentia affecting the formal factor of the nature, determining the specific nature just as the differentia specifica determines the generic nature, but as a material differentiating principle. What individuates the material individual, what marks it off as one in itself, distinct [pg 127] or divided from other individuals of the same specific nature, and incommunicable in that condition, is the material factor of that individual's nature—not, indeed, the material factor, materia prima, considered in the abstract, but the material factor as proximately capable of actual existence by being allied to certain more or less definite spatial or quantitative dimensions: “matter affected with quantity”: “materia quantitate signata”.[146]
In regard to material substances this doctrine embraces two separate contentions: (a) that the principle which individuates such a substance must be conceived as something positive, not really distinct from, but yet not contained in, the specific nature considered in the abstract; (b) that this positive aspect is to be found not in the formal but in the material principle of the composite corporeal substance.
To the former contention it might be objected that what individuates the specific nature cannot be conceived as anything positive, superadded to this nature: it cannot be anything accidental to the latter, for if it were, the individual would be only an accidental unity, a “unum per accidens” and would be constituted by an accident, which we have seen to be inadmissible; nor, on the other hand, can it be anything essential to the specific nature, for if it were, then individuals should be capable of adequate essential definition, and furthermore the definition of the specific nature would not really give the whole essence or quidditas of the individuals—two consequences which are commonly rejected by all scholastics. To this, however, it is replied that the principle of individuation is something essential to the specific nature in the sense that it is something intrinsic to, and really identical with, the whole real substance or entity of this nature, though not involved in the abstract concept by the analysis of which we reach the definition or quidditas of this nature. What individuates Socrates is certainly essential to Socrates, and is therefore really identical with his human nature; it is intrinsic to the human nature in him, a mode or aspect of his human substance; yet it does not enter into the definition of his nature—“animal rationale”—for such definition abstracts from individuality. When, therefore, we say that definition of the specific nature [pg 128] gives the whole essence of an individual, we mean that it gives explicitly the abstract (specific) essence, not the individuality which is really identical with this, nor, therefore, the whole substantial reality of the individual. We give different answers to the questions, “What is Socrates?” and “Who is Socrates?” The answer to the former question—a “man,” or a “rational animal”—gives the “essence,” but not explicitly the whole substantial reality of the individual, this remaining incapable of adequate conceptual analysis. The latter question we answer by giving the notes that reveal individuality. These, of course, are “accidental” in the strict sense. But even the principles which constitute the individuality of separate individuals of the same species, and which differentiate these individuals numerically from one another, we do not describe as essential differences, whereas we do describe specific and generic differences as essential. The reason of this is that the latter are abstract, universal, conceptual, amenable to intellectual analysis, scientifically important, while the former are just the reverse; the universal differences alone are principles about which we can have scientific knowledge, for “all science is of the abstract and universal”;[147] and this is what we have in mind when we describe them as “essential” or “formal,” and individual differences as “entitative” or “material”.
The second point in the Thomistic doctrine is that corporeal substances are individuated by reason of their materiality. The formative, specific, determining principle of the corporeal substance is rendered incommunicable by its union with the material, determinable principle; and it becomes individually distinct or separate by the fact that this latter principle, in order to be capable of union with the given specific form, has in its very essence an exigence for certain more or less determinate dimensions in space. Corporeal things have their natural size within certain limits. The individual of a given corporeal species can exist only because the material principle, receptive of this specific form, has a natural relation to the fundamental property of corporeal things, viz. quantity, within certain more or less determinate limits. The form is rendered incommunicable by its reception in the matter. This concrete realization of the form in the matter is individually distinct and separate from other realizations of the same specific form, by the fact that the matter of this realization [pg 129] demands certain dimensions of quantity: this latter property being the root-principle of numerical multiplication of corporeal individuals within the same species.
On the other hand, incorporeal substances such as angels or pure spirits, being “pure” forms, “formæ subsistentes,” wholly and essentially unallied with any determinable material principle, are of themselves not only specific but individual; they are themselves essentially incommunicable, superior to all multiplication or repeated realization of themselves: they are such that each can be actualized only “once and for all”: each is a species in itself: it is the full, exhaustive, and adequate expression of a divine type, of an exemplar in the Divine Mind: its realization is not, like that of a material form, the actuation of an indefinitely determinable material principle: it sums up and exhausts the imitable perfection of the specific type in its single individuality, whereas the perfection of the specific type of a corporeal thing cannot be adequately expressed in any single individual realization, but only by repeated realizations; nor indeed can it ever be adequately, exhaustively expressed, by any finite multitude of these.
It follows that in regard to pure spirits the individuating principle and the specific principle are not only really but also logically, conceptually identical; that the distinction between individual and individual is here properly a specific distinction; that it can be described as numerical only in an analogical sense, if by numerical we mean material or quantitative, i.e. the distinction between corporeal individuals of the same species ([28]).
But the distinction between individual human souls is not a specific or formal distinction. These, though spiritual, are not pure spirits. They are spiritual substances which, of their very nature, are essentially ordained for union with matter. They all belong to the same species—the human species. But they do not constitute individuals of this species unless as existing actually united with matter. Each human soul has a transcendental relation to its own body, to the “materia signata” for which, and in which, it was created. For each human soul this relation is unique. Just as it is the material principle of each human being, the matter as allied to quantitative dimensions, that individuates the man, so it is the unique relation of his soul to the material principle thus spatially determined, that individuates his soul. Now the soul, even when disembodied and existing after death, [pg 130] necessarily retains in its very constitution this essential relation to its own body; and thus it is that disembodied souls, though not actually allied with matter, remain numerically distinct and individuated in virtue of their essential relation, each to its own body. We see, therefore, that human souls, though spiritual, are an entirely different order of beings, and must be conceived quite differently, from pure spirits.
We must be content with this brief exposition of the Thomistic doctrine on individuation. A discussion of the arguments for and against it would carry us too far.[148] There is no doubt that what reveals the individuality of the corporeal substance to us is its material principle, in virtue of which its existence is circumscribed within certain limits of time and space and affected with individual characteristics, “notae individuantes”. But the Thomistic doctrine, which finds in “materia signata” the formal, intrinsic, constitutive principle of individuation, goes much deeper. It is intimately connected with the Aristotelian theory of knowledge and reality. According to this philosophy the formative principle or ἔιδος, the forma subtantialis, is our sole key to the intelligibility of corporeal things: these are intelligible in so far forth as they are actual, and they are actual in virtue of their “forms”. Hence the tendency of the scholastic commentators of Aristotle to use the term “form” as synonymous with the term “nature,” though the whole nature of the corporeal substance embraces the material as well as the formal principle: for even though it does, we can understand nothing about this “nature” beyond what is intelligible in it in virtue of its “form.” The material principle, on the other hand, is the potential, indeterminate principle, in itself unintelligible. We know that in ancient Greek philosophy it was regarded as the ἄλογον, the surd and contingent principle in things, the element which resisted rational analysis and fell outside the scope of “science,” or “knowledge of the necessary and universal”. While it revealed the forms or natures of things to sense, it remained itself impervious to intellect, which grasped these natures and rendered them intelligible only by divesting them of matter, by abstracting them from matter. Reality is intelligible only in so far forth as it is immaterial, either in fact or by abstraction. The human intellect, being itself spiritual, is “receptive of forms without matter”. But being itself allied with matter, its proper object is none other than the natures or essences of corporeal things, abstracted, however, from the matter in which they are actually “immersed”. The only reason, therefore, why any intelligible form or essence which, as abstract and universal, is “one” for intellect, is nevertheless actually or potentially “manifold” in its reality, is because it is allied with a material principle. It is the latter that accounts for the numerical multiplication, in actual reality, of any intelligible form or essence. If the latter is material it can be actualized only by indefinitely repeated, numerically [pg 131] or materially distinct, alliances with matter. It cannot be actualized “tota simul,” or “once for all,” as it were. It is, therefore, the material principle that not merely reveals, but also constitutes, the individuation of such corporeal forms or essences. Hence, too, the individual as such cannot be adequately apprehended by intellect; for all intelligible principles of reality are formal, whereas the individuating principle is material.
On the other hand, if an intelligible essence or form be purely spiritual, wholly unrelated to any indeterminate, material principle, it must be “one” not alone conceptually or logically but also really: it can exist only as “one”: it is of itself individual: it can be differentiated from other spiritual essences not materially but only formally, or, in other words, not numerically but by a distinction which is at once individual and specific. Two pure spirits cannot be “two” numerically and “one” specifically, two for sense and one for intellect, as two men are: if they are distinct at all they must be distinct for intellect, i.e. they cannot be properly conceived as two members of the same species.