Cursus Philosophicus Thomisticus, Secunda Pars Philosophiae Naturalis

Aristotle treats this difficulty in Physics VII, ch. 3¹, and many dispute it there. Yet this seems to be its proper place, where alteration is treated expressly.

We must suppose, then, that four species, or four divisions of species, are found in the category of quality, as we explained in Logic, q. 18,² namely habit and disposition, power and incapacity, passion and passible quality, figure and form. One may consult that discussion. We inquire which of these species are capable of terminating alteration first and per se.

Next I suppose that alteration’s being directed first and per se to some quality means nothing other than this: alteration reaches a quality as its term in such a way that no quality or other term intervenes at which that action terminates first. Motion is directed to a quality secondarily, however, when something else is reached mediately and secondarily through another thing that is touched more immediately. For example, by touching and changing heat or cold as an immediate term, health or sickness is reached as something resulting from the balance of cold or heat.

And so we ask whether all these species of quality, or only some of them, are what alteration touches immediately and per se; or whether only some can be touched immediately while the others are touched secondarily and mediately; and, if only some immediately terminate alteration, which ones they are.

Let there be one conclusion: Physical alteration, as we are speaking of it here, is per se and primarily only toward the third species of quality, that is, toward passion or passible quality.

This is Aristotle’s view in the cited place in Physics VII,³ where one may also consult St. Thomas,⁴ and his lecture 10 on On Generation I,⁵ as well as Summa Theologiae I–II, q. 52, a. 1, ad 3. We say “physical alteration” to exclude alteration understood broadly, which also includes instantaneous changes and spiritual or animal actions concerning habits or acts, which are not ordered to generation; there can be alteration in this broad sense around these, meaning the production of a quality. We say “first and per se” because physical alteration can indeed concern certain habits or dispositions, which belong to the first species, secondarily and consequently.

The foundation of this view is twofold. First, physical alteration, as was said,⁶ is per se and essentially ordered to substantial generation and corruption. But substantial generation and corruption require contrariety in dispositions, since forms are expelled and introduced through the contrariety of dispositions. Therefore, the alteration that serves generation must first and per se tend toward contrary qualities. Physical contrariety is found first and per se among qualities of the third species. This is clear both in the qualities that are contrary first—such as heat and cold, dryness and wetness, which are qualities of the third species—and likewise in the qualities that result from them as intermediate qualities and are contrary to one another; all these belong to the third species. It is also clear because these qualities, which have physical contrariety first and per se, transform their subject, which is changed above all by the contrariety of qualities; and they likewise affect the senses per se according to the contrariety they introduce. Therefore they must per se introduce a passion that changes the subject or sense. This constitutes the third species of quality, which is therefore called passion or passible quality, because it changes the subject and affects the sense either transiently or permanently. As St. Thomas says, Summa Theologiae I, q. 97, a. 2, properly speaking a passion is that by which something is removed from its natural disposition. Therefore, alteration, which first and per se concerns physically contrary qualities so as to be ordered to generation, directly regards only the third species of quality, which first and per se brings about a change in the subject and in the sense through passion.

The second foundation is taken from the Philosopher in Physics VII, ch. 3,⁷ where he proceeds through all the species of quality in which physical alteration occurs first and per se. The argument is brief: habits or dispositions are either spiritual or vital, pertaining to the apprehensive or appetitive powers, or purely bodily, such as health or beauty. If they are of the first kind, they are irrelevant here, because they are not acquired through the physical alteration of which we are now speaking, but through spiritual or animal action. Still, an alteration of the primary qualities may be presupposed as a prerequisite for these dispositions or habits, namely, insofar as appetite or imagination depends on some disposition of the organs, which is produced by bodily qualities. But if the habit or disposition is purely bodily, it still cannot be acquired first and per se through alteration, because such dispositions signify some suitability or unsuitability to the subject arising from a certain balance of the primary qualities, as is clear in health and beauty. Therefore alteration first terminates in those primary qualities and reaches health or beauty mediately. This is the force of Aristotle’s proof in the cited passage, where he says that there is no alteration per se toward habit and disposition because they are “toward something.” There is no motion per se and primarily toward a relation, as is proved in Physics V,⁸ but this should not be understood as though disposition and habit consisted in a predicamental relation, which alone cannot terminate motion per se. They are nevertheless like a predicamental relation in this respect: just as relations follow upon a foundation, so that motion first and per se terminates at the foundation and only consequently at the relation, these bodily dispositions result from the proper commensuration or proportion of qualities. Thus what alteration first touches is that quality as proportioned or tempered; the suitable or unsuitable disposition itself follows consequently.

As for the second species of quality, power and incapacity, it is clear that they do not first and per se terminate alteration—not only in the case of spiritual powers, which physical and bodily alteration does not touch, but also in the case of natural powers. There is no range of contrariety in powers, nor is there a more or less in them precisely as powers; moreover, powers are innate principles, proper attributes flowing from nature itself. Therefore they are not acquired through alteration first and per se, but follow upon generation. See what we shall say about this in the next question, art. 1.

Finally, physical alteration does not occur per se and primarily in the fourth species, figure and form. Figure does not admit a range of contrariety, but is like number: any addition or subtraction changes it, and so it has no range. Figure also results from the delimitation of quantity, and is therefore sometimes produced along with the production of quantity in the first generation of a thing, as when someone is born with a certain figure. At other times it results from the division of quantity, and then too it does not terminate alteration. Finally, it sometimes follows upon an alteration, as when the figure itself changes through excessive density or rarity, or something similar. In that case alteration does not terminate at it first and per se; alteration first and per se terminates at the quality that brings about the change in the delimitation of quantity.

You may say that this argument proves too much. It follows from it that alteration cannot occur first and per se toward certain intermediate qualities that result from primary ones, such as green or red color and other qualities that result from cold and heat; yet these belong to the third species of quality, as do density, rarity, and similar qualities, toward which alteration nevertheless occurs per se and primarily.

We reply that the case is different, because these secondary qualities that result from primary ones can themselves terminate alteration per se. They are not reached by the same motion that terminates at another quality first and reaches them secondarily; rather, they require a distinct motion in addition to the one that terminates at the primary qualities. For sometimes they arise without any alteration with respect to those qualities, as when something is whitened or darkened without any preceding cold or heat. And when these colors arise from the balance of the primary qualities, they arise through mixture, as do other secondary qualities. In mixture, however, the mixable qualities are corrupted, and thus a third quality is produced. Therefore alteration must not stop at the primary qualities as its term, with the secondary qualities merely resulting afterwards. Rather, the primary qualities are destroyed, and alteration tends toward the secondary quality as its terminus; since that quality is mixed from them, alteration toward it occurs per se. The case is different for a bodily disposition such as health, which does not result as a mixed quality from the corruption or mixture of the primary qualities, but from their proportion and commensuration. For health does not destroy heat or cold, but has them in due proportion.

The arguments are resolved.

First, it is argued that alteration per se does occur toward the first species of quality. For when health or beauty is acquired, it is acquired through some special motion or change. The change from sickness to health, which is healing, differs from the change from cold to hot, which is heating. There is also a different contrariety between sickness and health than between heat and cold, and a different terminus from which and to which. Therefore all the conditions for there to be distinct motions are present, especially since the change or action identified with health is not identified with heat. Such motion or change, insofar as it is toward health, can only be alteration and cannot pertain to another species of motion. Therefore alteration per se and primarily toward the first species of quality does occur, at least in the same way that alteration occurs toward secondary or mixed qualities, although they result from the primary ones.

This is confirmed because intensification and remission properly and per se occur in the first species of quality; therefore alteration does too, since intensification and remission are species of alteration, as we said in the preceding article. There is also true contrariety in that species, as between error and knowledge, vice and virtue, health and sickness. Wherever there is contrariety first and per se, there is a foundation for motion first and per se.

We reply, denying that the change toward sickness or health is formally different from the change toward the primary qualities from whose proportion or disproportion sickness or health arises. The contrariety between sickness and health, and the difference between the terminus from which and the terminus to which, are wholly consequent and materially different with respect to the alteration that occurs toward the third species. This follows from St. Thomas’s reasoning in Summa Theologiae I–II, q. 52, a. 1, ad 3, where he says: “Alteration is first in qualities of the third species, but alteration in qualities of the first species can occur afterwards.” He adds the reason: “For once alteration has taken place according to hot and cold, the animal then undergoes alteration according to healthy and sick.” Thus, although health and sickness are reached through the force of some change—which in reality is an alteration—because they are not reached as a term touched first and per se, but as something consequent, since it must always occur by means of an alteration of heat, cold, or another primary quality, this change, insofar as it touches health and is not identified with it, is not physical alteration first and per se, nor is health touched per se and immediately, but only consequently. Therefore the argument itself rather shows that alteration toward these dispositions occurs not first and per se, but consequently. The case differs for intermediate qualities of the same third species, which result from the mixture of primary qualities and thus require a distinct motion terminating at those intermediate qualities and corrupting and mixing the primary ones; that does not occur in the acquisition of health, as was said.

In confirmation, we reply that physical and bodily intensification and remission are species of physical and bodily alteration, but are not found in spiritual habits and acts. Hence physical alteration, of which we are now speaking, does not occur in them. Similarly, the contrariety found there is not physical or bodily contrariety, but contrariety so called in a broader sense, which is not ordered to generation and corruption.

Second, it is argued: In the second species, power and incapacity, true alteration can occur. A power can be weakened and made incapable through some new change; for example, sight that is sharp and vigorous in a young person can become weak in an old person, and one’s natural talent can also be dulled and rendered incapable by some accident. These changes cannot pertain to any other species of motion than alteration. Therefore alteration can concern power and incapacity first and per se.

We reply that a power which has once flowed from nature as from its proper subject can be removed only either by an opposing incapacity or by an extrinsic impediment. The first cannot occur while one and the same nature remains in the same state; for the same nature cannot at one time give rise to a power and at another to an incapacity, just as a human being gives rise to the capacity for laughter and not to its incapacity. If the same nature were to give rise to a power in one state and an incapacity in another, as different properties commonly belong to it in different states, these would still not terminate alteration first and per se, but would result from a new emanation. If, however, incapacity consists in an extrinsic impediment to the same power, alteration concerns that extrinsic impediment, not the power itself. For an extrinsic impediment pertains to some quality of the third species, by which the proper disposition of the organ is altered so that the power, which depends on the organ’s disposition, cannot operate properly while that indisposition remains. For this reason sight that was sharp becomes weak and natural talent is dulled: the organ of sight is impeded by some imbalance among its dispositions. Likewise the imaginative power, or phantasy, is rendered ill-disposed to supply the intellect with what pertains to natural talent. Alteration can occur per se toward these dispositional qualities.