Cursus Philosophicus Thomisticus, Secunda Pars Artis Logicae

This difficulty is related to the preceding one, and from it we understand more fully how a species can be predicable of many, even if they are not possible because of the mode of individuation. Since two things are considered in both genus and species—namely, the nature they actually express and the many things to which they are in potency—it is certain that both genus and species, with respect to the nature they actually express, can be preserved in one species and one individual. For genus communicates its whole essence to each inferior; therefore the whole nature of genus and species is preserved in each. Hence St. Thomas says in Summa theologiae I, q. 77, art. 1, ad 1, that “the universal whole is present to each according to its whole essence and power, as animal is present to human being and horse.” Therefore the whole essence of genus is preserved in each species.

THE WHOLE DIFFICULTY is thus reduced to this: can genus, with respect to the potentiality and order it has toward many, be preserved with respect to one species, even if the others were impossible? For if they are possible, even if they do not in fact exist, it is certain that the genus's potency toward them is preserved, since it does not depend on their existence. In fact, after Judgment Day, in the whole genus of animal there will be only one species, human being; and this could also have happened from the beginning. We speak similarly of species according to its potency and aptitude to exist in many. The question is not about the intentions themselves, but about the aptitude and potency for many, which is their foundation. For an intention is a relation that follows the nature of its foundation.

Some therefore judge absolutely that genus can be preserved in one species and species in one individual. The reason is the same in both cases, because both are equally universals, and a universal is one in many. Therefore, if multiplicity for a species suffices only on the side of the mode of conceiving, although not on the side of the thing conceived, as we said in the preceding article, the same will suffice for genus. Others, on the contrary, think that neither genus nor species can be preserved in only one inferior, because it is essential to each universal to be divided by many differences, since it is one of many; therefore, if the many are lacking, the universal is lacking. Finally, others distinguish between genus and species: to preserve genus as a potential whole, they think many species are required; but to preserve species, many individuals are not required. On these opinions see the Carmelite Course, disputation 6, question 2.

This last opinion is more common and is undoubtedly St. Thomas's in his commentary on Posterior Analytics I, lect. 12¹, where he says: “It is not possible to find a genus of which there is only one species. For genus is divided into species by opposed differences. But if one of two contraries is found in nature, the other must also be found, as is clear from the Philosopher in On the Heavens II²; therefore, if one species is found, another is found as well. A species, however, is divided into different individuals by the division of matter. It can happen that the whole of the matter proportioned to some species is comprehended by one individual, and then there is only one individual under that species.” The holy Doctor teaches the same in Sentences I, dist. 19, q. 4, art. 2, body³.

THE BASIS of this opinion is drawn from two propositions set down by St. Thomas. First, genus is divided by opposed differences. Second, if one opposite or contrary is found in the nature of things, the other is found as well.

The first proposition is clear, because genus is contracted by formally diverse differences, that is, by forms incompatible with and distant from one another in the same genus. But opposition or contrariety consists in there being forms distant from one another in the same genus; if they are maximally distant, the contrariety is perfect. That genus is divided by formally diverse differences is clear because genus is divided by differences that contract it to constitute a species. Therefore, genus must express a nature capable of being actualized and contracted by formal differences that complete its actuality and formally constitute its essence. Hence, if it has several differences, they must be formally, not merely materially, diverse—that is, diverse in the very formal notion of quiddity—and therefore they must be opposed, as formally incompatible.

The second proposition is proved by St. Thomas himself in On the Heavens II, lect. 4⁴, because contraries have the same matter and subject; otherwise they would not expel one another if they did not concern the same subject. Therefore the matter or subject of one contrary must have potency for the other contrary. If, then, one contrary exists in the nature of things, the other is also possible, because there is a potency capable of receiving it. If it were impossible, this very fact would destroy the receptive potentiality for it in matter or genus, since there would be potentiality to receive only one. Thus the genus's potentiality for many would be destroyed, since it is for many as contraries and formally opposed things.

From these propositions the difference between genus and species is clearly deduced. Genus is related to specific differences as potential matter to actual and formally opposed or incompatible forms. Species, however, expresses an order toward many things that differ only materially and are incompatible only materially. Thus it is not related to individuating differences as matter to form, but rather as form to material division. What functions as matter, if it is communicable to many, must presuppose the possibility of those to which it is communicable. But what functions as form is communicable to many through the very character and concept of form, even if communication can be impeded by a defect in the receiving matter. The reason is that matter, and what belongs on the side of matter, is rather a principle of incommunicability in itself, just as it is a principle of limitation and restriction. But since matter is the ultimate subject, beyond which there is no communication, if matter is communicable to many, this is because those many are possible in relation to such matter. Thus the potentiality of matter for many is taken from the possibility of forms in relation to some subject or matter. If matter is communicated to form, this is more so that it may be perfected in itself by form than that it may communicate itself, since communicating itself is proper to the good. Matter, however, is not good in actuality, since it is neither perfect nor actual; and, as St. Thomas says in Summa theologiae I, q. 5, art. 3, ad 3, prime matter is not appetible but appetitive. Hence form desires matter not so much as matter, but rather to be in matter.

Therefore, for matter to be communicable to many means nothing other than that it can be actualized and perfected by many. Thus the potentiality of matter or genus for many arises from the plurality of forms that can perfect it. Form, by contrast, by its very character as form—which is act and perfection—is communicable to many insofar as it itself is concerned: for it is perfection and act, and perfection is good; good, as good, communicates itself. Therefore its communicability in itself does not depend on there being many recipients; it has this from the character of form and act. Hence St. Thomas says in On Interpretation I, lect. 10⁵, “every form that is naturally apt to be received in matter is, in itself, communicable to many matters.” And in Summa theologiae I, q. 3, art. 2, ad 3, and his commentary on Metaphysics VII, lect. 15, § Ponit aliam rationem⁶, he says universally that “any form, considered in itself, is naturally apt to exist in many.” Since species is taken from form and, by the very mode of conceiving it, expresses an essence formally complete, it is not incompatible to conceive it as communicable to many, even if, because of a defect in the receiving and materially dividing matter, it cannot always be communicated in actual exercise, as we said in the preceding article concerning angelic species. Therefore, species as such, even with respect to its communicability to many, does not depend on many individuals; genus, however, depends on many species.

THE ARGUMENTS ARE ANSWERED.

First it is argued to prove that genus can be preserved in only one species: in one species alone one can take an indeterminate and potential degree or character, and an actual and determinate character or degree; therefore genus and difference can be taken.

The antecedent is clear, because that species would be in a category, since it would be a created thing. Therefore it would have a higher and lower degree and, consequently, something determinable and determinate, since not all its predicates would have equal actuality and determination.

THE REPLY is that the species would indeed be in a category by reason of its limited nature and would have a higher and lower degree—not by a greater and wider superiority with respect to inferiors, but as less determinate and actual, or more potential, on the side of quiddity than the contracting difference. Thus it would not be universal generically, although it would have a nature more potential than the difference, as genus does. Its potentiality, then, would concern only one form, not be indifferent to many, as the potency of a soul or angel to receive intellect; this is not a potentiality for many, but only for one.

When it is objected that this generic predicate would not be equal to the specific and differential predicate, and therefore would be superior to them as genus:

The reply is that it would not be equal in actuality, because the difference would actualize it, but it would be equal in extension, because it would not extend to more things than species and difference. Generic universality, however, requires extension to many in the character of a potential whole, even though the nature it expresses is more imperfect and potential than the contracting difference in the character of quiddity.

Second it is argued: If the whole potentiality of genus could not be preserved in one species, then neither could it be preserved in two, ten, or any other definite number, because there is no greater reason why that potentiality should be exhausted by two species than by twenty or a hundred. Thus every genus would require infinitely many species, and the whole potentiality of genus could not be preserved, by absolute power, in one or two species, even though the whole potentiality of matter can be satisfied by one incorruptible form. Indeed, on this reasoning it would follow that species could not be preserved in one individual either, because it is in potency to many individuating conditions, which cannot all be preserved in a single individual. Therefore, just as genus is not preserved in only one species because it is in potency to many differences, neither is species preserved in one individual, because all individuating conditions cannot be gathered into one.

THE REPLY is that the potentiality of genus is preserved sufficiently by the very fact that it has many species, whether their number is determinate or infinite, for we are not discussing that. Therefore, at least two species under one genus are required and suffice; and, for the reason given, its extensive potentiality cannot be preserved, even by absolute power, with respect to only one species.

As to the example of matter, we say that either this matter is capable of many corruptible forms or it is capable of only one incorruptible form, as many think of the matter of heaven. If the latter, the potentiality of contrariety and extension to many is not preserved in that matter, but only the potentiality for actualization and informing, which occurs through one form. If the former, that matter always remains in potency to many forms by which it can be informed, even if in fact it is not in a state of change toward them, when it has an incorruptible form by which it is satisfied with respect to changing into other forms, though not with respect to its capacity for them.

As to the example of species in relation to many individuals, the reply is that it is true that one individual cannot have all the properties and individuating differences of a species, if they are in fact possible; but in one individual it has a nature which, by the concept of form and act by which it is constituted, is not incompatible with being communicable to many individuating differences, even if those differences are impossible because of a defect in matter. Genus, however, by being in one species, is not communicable to many species if those species are impossible, because matter is not in itself a principle of communicating to many, but of receiving many. Therefore, if those are impossible, the potentiality to receive them does not remain. The same applies to genus, whose potentiality is assimilated to matter in its relation to forms or formal differences.

Finally it is argued: If a species is preserved in one individual, it either has an incompatibility with many essentially attached to it or it does not. If it does not, then those many are possible, and thus the supposition that only one individual is possible is removed. If it has an intrinsic incompatibility, then it cannot, even according to the mode of conceiving, be taken as communicable and universal to many; thus there would be no difference between it and genus.

It is confirmed: In that case species and individual are not distinct, since only one individual is possible. Therefore the indifference to many required for the universality of species is not preserved in it. Or, if indifference is found because it is a higher predicate, we will say the same of a generic predicate in only one species.

THE REPLY is that even if species has an incompatibility with many individuals essentially attached to it, its character of universality can be preserved, if it has that incompatibility not from the concept of its nature as nature, but from its mode of individuation, which is contained radically in the specific nature itself, as we said in the preceding article. Thus, it is not incompatible to conceive such a nature inadequately and under the precise concept of nature and form as communicable to many, since that precision and inadequate concept do not entail incompatibility, even if in reality it is incompatible on account of another principle that also pertains to the essence itself, namely, that it lacks matter in whose different parts a different individual nature could be received.

To the confirmation, the reply is that this specific nature is distinguished by reason alone from that one individual. Nevertheless, it is said that indifference and potentiality for many fundamentally remain in such a species, but not in genus—not only because it is a higher predicate, but because it is such a higher predicate, namely, by way of a formal quiddity which, according to the properties of form, is communicable to many from the very concept of form and nature, even if there are no things to which it could be communicated. Genus, however, by the force of its precise concept, does not express communicability to many as form does, but as matter does; unless many forms are possible, it has no potentiality to receive them.

From this the other objection is also resolved: how can species, being a potential whole with respect to individuals, be preserved in only one individual, which is a part of it, since every whole is greater than its part?

The reply is that species existing in only one individual is a potential whole not only with respect to that individual, but with respect to many, to which it is not incompatible to be communicated by the force of its formal concept, even if in reality many things to which it could be communicated are not possible. Therefore we do not say that species is preserved with respect to only one individual, but that species existing in one individual is not incompatible with being conceived as communicable to many, insofar as this follows from the mode of conceiving that form or nature.