Commentaria in Summam contra Gentiles, Liber II

Since it has been shown that separate substances are specifically distinct, how genus and species are found in them, because this presents a difficulty, remains to be inquired into ¹. On this point Saint Thomas does three things: first, he shows whence the difficulty arises; second, he explains the proposed question ²; third, he draws certain corollaries ³.

I. As to the first, he says that from this a difficulty arises: since separate substances are not composed of matter and form, genus cannot be taken in them from what is material, nor the specific difference from what is formal, as happens in material things; and therefore it does not appear according to what genus and specific difference can be taken in them.

II. As to the second ⁴, he first lays down that, since the diverse species of things possess the nature of being by degrees — as is evident both in the first division of being, which is by substance and accident and by act and potency, and in the other divisions of genera into species; on account of which it is said in VIII Metaph., text. 10, that the distinctions ⁵ of things are like those of numbers, in which a unit added or subtracted varies the species — the ratio of a determinate species consists in this, that the common nature is placed in a determinate degree of being.

This supposition being granted, because we come to knowledge of immaterial things from material things, he first shows whence genus and difference are taken in material things; second, whence in immaterial things. He says therefore first that in things composed of matter and form, the account of genus is taken from what is material, but the account of difference from what is formal: because in those things form is as it were a terminus; and that which is determined by it is matter or the material. — From this it follows first that from genus and difference one thing results just as from matter and form. — It follows second that the difference does not add an extraneous nature above the genus, but is a certain determination of it itself, as is clear in this genus animal and this difference two-footed: just as one and the same is the nature which is constituted from matter and form. — From this it further follows that the determination which the difference imports happens to be caused in genus and difference from another principle than the nature of the genus: from this, I say, that the nature which the definition signifies is composed of matter and form, as of the terminated and the terminating.

Second, he shows whence genus and difference are taken in separate substances. And he says that the ratio of genus is taken from the very ratio of the nature, while the difference is taken from its determination according as it exists at such a grade of being. The reason for this is that a simple nature is terminated of itself, and there is no taking in it of a part that is terminated and a part that terminates.

III. As to the third point, three corollaries are drawn ⁶. The first is, that in infinite nature, as it is divine, one can take neither genus nor difference.

The second is, that among the separate substances there are not two that are equal in rank: since all are distinguished by species, and diverse species in them are taken according to diverse degrees. — This he also confirms by the authority of Job 38, "Do you know" etc.; and of Dionysius, chapter 10 of the Celestial Hierarchy.

The third is, * that the error of Origen is excluded, who held that from the beginning all spiritual substances were created equal, among which he also counts souls, and that their diversity arose from a diversity of merits.* For from what has gone before it is evident that this is false.

IV. But concerning this declaration a doubt arises. For according to this doctrine, two things are said of genus and difference in things composed of matter and form. One is that they are taken from something formal and something material: an example is given of the sensitive and intellective natures, from one of which is taken the genus of man, which is animal, and from the other the difference, which is rationale. The other is that the difference adds nothing extraneous to the genus.

For from these it follows that in material things the nature from which the genus is taken, which stands as material and determinable, and the nature from which the difference is taken, which stands as formal and determining, are one and the same nature in reality, as the sensitive and intellective nature in man; but they are distinguished by reason, inasmuch as the same nature, insofar as it stands in the manner of a potentiality and of the determinable, is distinguished by reason from itself insofar as it stands in the manner of a form and of the determining.

But the same thing is found in immaterial things. For, as is stated in the First Part, q. 50, a. 2, ad 1, in them one and the same nature, considered in one way, is determinable, and, considered in another way, is determining; and from that nature as determinable, and consequently potential, the genus is taken; but from that same nature as it is determining and formal, the difference is taken. For genus, wherever it is posited, signifies something determinable, and difference something determining. Therefore it is not fittingly maintained that there is a difference in the way genus and difference are taken in material things and in immaterial things, on the grounds that in the former they are taken from something formal and something material, while in the latter they are not. Indeed, from the explanation of the mode found in material things, a similar mode ought to have been concluded to hold in immaterial things.

V. For the clarification of this, and of what St. Thomas touches upon in this subtle exposition, it must first be known that we can speak of genus in two ways: namely, in the manner of first intentions, for the very nature signified by the name of first intention, to which the intellect attributes the intention of genus, as for that genus which I call animal; and in the manner of second intentions, namely for the very relation signified by this name genus, which the intellect attributes to the nature considered without limiting differences.

When, therefore, we ask from what genus and difference are taken, we do not ask about genus and difference second-intentionally, but first-intentionally: for we ask from what is taken that ratio to which the intellect attributes the intention of genus, and from what is taken the ratio to which the intention of difference is attributed.

2. It must be known, secondly, that each species contains that which it has in common with others, and beyond this, a determinate grade in what is common to itself and to others. Now these two in the species are one and the same thing, namely, the specific nature: just as the sensitive nature in man, by which he agrees with brute animals, and the intellective nature, by which he differs from them, are not really distinct in man, but are the same as humanity. But although these two are one thing, the intellect can nevertheless form several concepts of that thing: one of which applies to it insofar as it includes what is common to many, and this is the generic concept; another applies to it insofar as it contains the grade by which it is distinguished from others under that common element, and this is the differential concept; and still another applies to it insofar as it embraces both perfections at once, and this is the specific concept. And just as the intellect conceives one and the same thing in diverse ways, so too does it signify it by diverse names, through the mediation of diverse concepts, and attributes to those names diverse intentions, namely, of genus, difference, and species.

This, however, is found not only in things composed of matter and form, but also in immaterial substances. For since among them there is specific distinction, they also have something in which they agree; and something by which they are distinguished from one another according to determinate degrees of being.

3. It must be known, thirdly—as can be gathered from the doctrine of St. Thomas in De Spiritualibus Creaturis, a. 1, ad 24; and in the Treatise De Ente et Essentia; and also II Sent., d. III, q. 1, a. 5—that in material things there are two sources from which the notion of genus is taken, and two from which the notion of difference is taken: namely, that from which they are taken proximately, and that from which they are taken remotely and originally. The proximate source from which they are taken is the very nature of the species, which is naturally apt to ground diverse concepts, as we have said. And thus genus and difference are taken proximately and immediately from one and the same thing: for instance, from that entity which is humanity are taken animal and rational, and both animal and rational signify it, though under one and another aspect—animal indeed as it is a sensitive nature, but rational as it is intellective. — But what first and originally grounds genus and difference is matter and form. For matter receives diverse perfections from one form in a certain order, just as it is naturally apt to receive diverse forms in an ordered way: so that under one perfection it is compared to another as potential to actual, as perfectible to perfection, and as determinable to determining. Form, however, is that which terminates the potentiality of matter, giving to it esse and completion. And thus the imperfect nature has from matter that it be possible for perfect esse, inasmuch as the potentiality of matter is not completed by that imperfect esse, but rather is disposed toward perfect esse: just as in the process of generation it is disposed by the imperfect form toward the perfect form. But it has perfect esse from form, namely that it be actuality and termination, inasmuch as form by such esse terminates and completes the potentiality of matter and its imperfect esse. — And on this account he rightly says here that genus is taken from matter in material things, or from the material: because, namely, it is taken proximately from the whole nature of the species as potential, as from a nature signified by the very name of the genus; but it is taken remotely and originally from matter, as from the first origin of the potentiality of the nature. Similarly, difference is taken proximately from that same specific nature as actual and determining, as from a nature signified by the name of the difference: but it is taken remotely and originally from form, as from the first origin of actuality.

In immaterial things, however, there is no distinction between the proximate and remote foundation of genus and difference, since there is no composition from several parts there: rather, the ratio of genus is taken from the nature itself, insofar as it is determinable by a conceivable concept; but the ratio of difference is taken insofar as it is determinable by a determining concept. And this is what St. Thomas intends here, when he says that from the very ratio of the nature, namely as considered absolutely and indeterminately, the genus is taken; but from its determination according as it exists in such a grade of being, its specific difference is taken.

VI. From these things it is clear that genus and difference agree in two ways both in material things and in immaterial things, and in one way they differ. They agree, first, in that in both cases the genus signifies a determinable nature and the difference a determining nature, which belongs to genus and difference of themselves. — They agree, second, in this: that there is one and the same nature according to reality, differing only according to reason, from which in both cases the reason of genus and the reason of difference are immediately taken. — They differ, however, with respect to what happens to genus and difference as they exist here. For in material things, genus and difference are taken primordially and originally from diverse parts, namely genus from matter and difference from form. In immaterial substances, however, they are not taken in any way from diverse parts of the species, since these are simple natures; rather, the very nature of the species alone, as diversely conceivable and signifiable, is that from which both genus and difference are taken.

To the doubt, then, it is said that indeed, as we have already said, the acceptance of genus and difference in immaterial things does not differ from their acceptance in material things with respect to the thing from which they are proximately taken, as the argument proves; nor does St. Thomas intend to deduce this. But they differ only with respect to the first origin and first root of such an acceptance: for in material things matter and form are the origin of genus and difference, but not in immaterial things. And this is the difference that St. Thomas deduces from his explanation.

VII. But it still remains to inquire, when the genus is taken in intellectual substances from the very intellectual nature considered indeterminately, while the difference is taken from the determination to such a grade of being, in what sense that determination to a certain grade of being is to be understood.

2. For the evidence of this, it must be considered, according to the doctrine of Saint Thomas in II Sent., at the place cited above; and in the Treatise on Being and Essence; and in the Treatise on the Nature of Genus ⁷, that since the ratio of substance, which is the predicamental genus, according to the mind of Avicenna, is to have esse other than its quiddity, per se and not in another, this is common to every substance existing in the genus: that in it there is a composition of essence and esse. And because essence, distinct from esse, is compared to its esse as potency to act, therefore in every substance existing in the genus there is something potential and something actual.

Since, then, genus signifies something potential, it must be taken from the very quiddity itself, which is potential with respect to esse. Difference also, since it cannot be taken from esse, which is actual—indeed, act—because that from which the difference is taken must belong to the quiddity and essence of the thing, while esse is not part of the quiddity of a created thing: it is necessary that the difference likewise be taken from the quiddity itself, but in a different way. For quiddity can be considered absolutely and indistinctly, as potential with respect to esse; and it can be considered as proximate to esse itself, namely as determined and established at some degree of proximity to esse. From the quiddity insofar as it is absolutely potential is taken the ratio of genus; from the quiddity insofar as it has a determination by which it approaches esse is taken the difference.

And this is common both to material and to immaterial things. But a material thing differs from an immaterial one in this, that the potentiality of the quiddity has its origin from matter, which is the first recipient and the first subject; while the determination of the quiddity is taken originally from form, whose role it is to determine the potentiality of matter. Therefore in them genus and difference are taken not only from the quiddity as determinable and as determined, but also originally from matter and from form, as we showed above ⁸ — In immaterial things, however, since they have no matter and form, genus is taken from the quiddity itself and intellectual nature taken absolutely and indistinctly, as it is potential with respect to esse; but difference is taken from that same quiddity as thus determined and proximate to esse.

3. From these things the proposed question is made clear. For since their difference is taken from recession from potentiality and nearness to esse, the specific degree in them will be taken according to greater and lesser nearness to esse. For the more any intellectual nature recedes from potentiality and draws nearer to esse and to act, the nobler it is and of a higher grade, as being nearer to the most perfect being, which is God, through a greater participation in divine esse; but the more it stands distant from esse and actuality, the more imperfect is its grade, as being more removed from the first act and participating less in divine esse. But, as Saint Thomas says in the Treatise On the Nature of Genus ⁹, we cannot know these grades: but only those know them who contemplate their own nearness to God and their distance from composite and corruptible things.

VIII. Further, in the very course of Saint Thomas's argument two things must be noted. The first concerns that proposition: At once in the first division of being there is found one thing perfect, namely being per se and being in act, and another imperfect, namely being in another and being in potency. For this is not to be understood as though one and the same division of being were by substance and accident, and by act and potency; but because these are among the first divisions of being, by which it is divided according to determinate modes of esse. He sets forth both divisions as one first division because these divisions accompany one another: for in every genus, whether of accident or of substance, potency and act are found, as is said in Book IX of the Metaphysics ¹⁰

2. The second concerns this proposition, Just as one and the same is the nature constituted from matter and form, so difference does not add some extraneous nature above the genus. For this likeness can bear a twofold sense. The first is that genus and difference be compared to matter and form, which constitute one nature. And thus Saint Thomas does not take it. For although from those there is made one nature, matter and form are nevertheless not one thing/res. Therefore from this it could not be argued that genus and difference are one thing, as Saint Thomas wishes to hold; but only that from genus and difference there is constituted one thing according to logical consideration, namely the species, just as in the esse of nature one thing is constituted from matter and form.

Another sense is possible, so that a comparison may be made between genus and difference and the nature constituted from matter and form. For since it has been said that in material things the genus is taken from that which is material and potential, and the difference from that which is formal and determinate, and that matter is that from which the materiality and potentiality of the nature are taken, while form is that from which determination is taken: if that potential element taken from matter were to constitute itself apart from matter, and that formal and actual element taken from form were to be constituted apart from form, such that there would be two natures, then it would certainly be true that the difference, which conveys what is formal, would add an extraneous nature to the genus. But because one and the same nature is constituted from matter and form, and derives the character of the potential from matter and the character of the formal from form, therefore the difference itself, which is taken from the formal, does not add an extraneous nature above the genus, which is taken from the potential and the material. And this is the true sense which Saint Thomas intends in this comparison.