Cursus Philosophicus Thomisticus, Secunda Pars Philosophiae Naturalis

The name “alteration” is derived from “other”; it is said as though it makes something other. As is said in the chapter on Difference,¹ being other is one thing, being another is something else. For “other” indicates accidental difference, while “another” indicates substantial difference. Thus we can take the name “alteration” in the broadest sense for every accidental change in any category of accident. But we are not now speaking of alteration taken so universally. It is therefore taken more strictly for change in quality, since there are particular changes in quantity and place, namely increase and local motion. In qualities, however, a thing becomes other most of all, especially when through them it is ordered to some corruption; for corruption most of all makes a thing other.

Therefore, still taking the entire category of quality, we must distinguish that some qualities are spiritual and some bodily; some natural and some intentional; some have contrariety and some do not. Those that are spiritual or do not have contrariety are not ordered to physical corruption or generation. Thus, although in a broader sense they can be called alterations, they are not called physical alterations, which we chiefly treat here, because they are not ordered to corruption and generation.

With regard to qualities that do have contrariety, one can proceed in two ways: by way of change or by way of motion. By way of change, the process is from privation to form, as from nonwhite to white, which is accidental generation. In that case it is not from one contrary to another, although the quality itself has a contrary. By way of motion, the process is from one positive term to another positive term across a range and distance from one to the other. It is clear that this occurs in qualities, as we showed in Physics q. 19,² as with heat and cold, whiteness and blackness, and similar things; in that case there is true contrariety. Similarly, a positive distance and range from something positive to something positive is found in the more or less of the same quality. All this occurs while the same sensible subject remains. Therefore it has all the conditions required for motion strictly so called, as distinguished from change; and this is chiefly what we treat here.

On this supposition, Aristotle defines this alteration, which is motion, in this book, On Generation and Corruption I, text 23,³ as follows: “Alteration occurs when, the sensible subject remaining, it is changed in its passions or in intermediate motions between contraries.” From this some derive the following definition of alteration: “Alteration is motion toward an intermediate or extreme sensible quality,” that is, toward a quality having a range of contrariety. “Motion” is said to exclude instantaneous changes, the chief of which is generation itself. “Toward a quality” excludes the other species of motion, which concern quantity or place. “Sensible quality” excludes motions concerning spiritual qualities, such as habits or acts. “Intermediate or extreme,” that is, having contrariety and a range, excludes qualities that do not have contrariety, such as light, figure, and similar things. Therefore, although other changes toward quality can in a broad sense be called alterations and reduced to them, alteration properly regards contrary and corruptive qualities, because by its nature alteration serves generation and corruption as their instrument and concerns qualities that serve generation and corruption, which are contrary qualities. Thus Aristotle, in this book,⁴ lecture 2 of St. Thomas’s commentary,⁵ draws this inference against the ancient philosophers: if it is impossible for fire to come from water, and one element from another, then it will also be impossible for black to come from white, and likewise for other qualities; thus, if generation is destroyed, alteration is destroyed. Therefore alteration is ordered per se to generation. Hence St. Thomas rightly gathers all the conditions of alteration in Sentences III, dist. 15, q. 2, a. 1, question 1,⁶ saying: “For there to be alteration, on the part of what is altered it is required that it be a thing subsisting per se, since otherwise it cannot be a subject of motion; that it be a body, since only such a thing is moved; and that it have a nature subject to contrariety, since alteration is motion between contrary qualities.” On the part of the terms, it is required that once one quality is expelled another be introduced; for in this way one passes from quality to quality.

From these points the difference between alteration, generation, and the other motions is derived. Alteration differs from the other motions on the side of its term, because increase is toward quantity and local motion toward place. It differs from substantial generation both on the side of the term, because generation is toward substance, and on the side of the subject, because the subject of generation is prime matter, while that of alteration is a sensible subject, or matter informed by a form; it also differs in the kind of change, because generation is instantaneous whereas alteration is successive, and in its starting term, because generation is from privation while alteration is from a positive contrary term. Finally, it differs from generation in a qualified sense, because the latter does not occur through motion or from a positive term, but from a privative one, as when something white comes to be from what is nonwhite.

But you will object, to prove that alteration is not ordered per se to generation: The production of whiteness and other colors is a true alteration, and is not ordered per se to substantial generation. Likewise, the acquisition of figure, illumination, and darkening are alterations, yet they are not ordered per se to substantial generation.

This is confirmed, because otherwise, if substantial generation were impossible, alteration would also be impossible, since it is essentially ordered to generation. But the consequence is false; therefore, so is the premise. The minor is proved because alteration does not depend per se on a change of substance, although it depends on substance as its subject. This is clear in incorruptible things, such as heaven, the bodies of the blessed, and the bodies of the damned after Judgment Day, in which generation and corruption are impossible. Yet alteration will occur in them, as illumination and darkening in heaven, and condensation and rarefaction, for some parts of heaven are denser and others rarer. Indeed, there could even be a contraction, since speech among the blessed in heaven could not occur except through contraction of the heavenly body itself, as St. Thomas admits in Sentences II, dist. 2, q. 2, a. 2.⁷ For there is no air there to be contracted when the voice is formed, nor could it be formed without some condensation of the contracted body, since the separated part does not penetrate another but is condensed. In the bodies of the blessed there will be breathing, speech, touch, and taste, which do not occur without alteration. In the bodies of the damned there will be heating and cooling, by which they will be tortured. Therefore alteration occurs without being ordered to generation. Finally, if human beings had existed from eternity, generation would not be possible in them, as we proved in Physics VIII,⁸ yet alteration would occur in them, because they would be nourished, breathe, speak, and so on. Therefore not every alteration is ordered per se to generation.

We reply that alteration which is motion and occurs between contraries is ordered per se to generation, as was said. As for the proof to the contrary concerning whiteness and other colors, although they do not immediately serve generation as its active dispositions, they can nevertheless be ordered to it mediately and in their cause, because these colors are caused by the balance of the primary qualities, which serve generation and corruption more immediately. Therefore colors, as consequent upon such qualities, are also ordered mediately to generation and in their cause. The acquisition of figure sometimes occurs through alteration, as when parts are changed by rarefaction, condensation, or another quality so as to lose or change their figure; then that acquisition of figure pertains mediately to alteration and is ordered to generation in that way. At other times, however, a change of figure occurs through local motion alone, as when division or joining of parts through local motion brings about a new delimitation of quantity and a new figure results. Since this does not follow upon alteration, it is not ordered per se to generation. We have already said⁹ that illumination and darkening are not alteration strictly so called, but alteration in a broad sense; in that sense they are not ordered per se to generation as alteration is when it occurs per se between physical contraries.

In confirmation, we deny the minor. For alteration requires not only substance as its subject, but also a change of substance, since it is a kind of beginning of substantial change: substance depends for its preservation on accidents as dispositions, and thus the removal of dispositions is the beginning of corruption.

As for the proof, we reply that there is no alteration strictly so called in heaven, which is alteration between contraries. Illumination and darkening are not of themselves corruptive alteration, although in lower things they may accidentally be followed by alteration of corruptive qualities, insofar as such things depend on the influences of heaven, which act through light. Condensation and rarefaction do not occur in heaven either. For although some parts are found to be denser—namely, the starry parts—and others rarer—namely, the transparent parts—they have this from the beginning of their creation, as they have their other proper accidents; they do not now acquire it through alteration.

As for what is adduced concerning the bodies of the blessed, we reply that all these things occur without a motion of alteration. Breathing and speech occur through the local motion of emitting and striking air. Breathing will not be necessary for the blessed to cool the heart and temper its heat, as it is for us, because those bodies, being incorruptible, are not changed by heat through alteration. To speak, it is enough to strike the air and divide it by local motion. How this occurs in heaven is very difficult for theologians, given the incorruptibility of heaven discussed in the books On Heaven.¹⁰ As for St. Thomas’s account of contraction of the heavenly body during the speech of the blessed, the holy Doctor does not state this as his own view, but on the supposition of others who hold that condensation and rarefaction can occur in heaven; he nevertheless says that they apply to heaven only equivocally. It seems more probable, however, that voices are formed in the air within the throats and mouths of the blessed, of whom Psalm 149 says:¹¹ “The high praises of God are in their throats.” Nor is it a difficulty that some air enclosed in the bodies of the blessed should ascend above heaven, although it is elemental, just as the blessed bodies themselves virtually contain the elements because they are mixed bodies. Although this air is incorruptible, like the other elemental bodies after Judgment Day because of the cessation of heaven’s motion, it can nevertheless be condensed or rarefied by compression or dilation of its parts through local motion, without another alteration. So too, if water is moved then, its parts can be compressed without alteration by condensation, as we shall explain more fully below, q. 7,¹² Once a voice has been formed in that air, it is conveyed to the hearing of another blessed person through heaven as a medium by means of intentional species, not through physical alteration or contraction of the heavenly body by sound. The remaining alterations in the bodies of the blessed, concerning passions and sensations, will be only animal actions of the senses through intentional species or elicited acts, not natural and corruptive alterations, as St. Thomas teaches in Sentences IV, dist. 44, q. 2, a. 1, question 1, ad 3.¹³

Concerning the bodies of the damned, we say that they will be acted upon not by natural alteration, which will then entirely cease when the first alterer ceases—that is, the motion of heaven, by whose power other lower things alter—but by intentional alteration through the reception of species. This will not cease, because it does not depend on the motion of heaven but on light and other intentional qualities. Thus the fire of hell, through tangible species, will cause a very great sensation of itself in those bodies. On this see St. Thomas in Sentences IV, dist. 44, q. 3, a. 1, questions 2 and 3.¹⁴

Of the human being created from eternity we say that, just as that person would have lacked generation for an infinite time, so too would he have had to lack the motion of alteration and the change that occurs through some generation for the same length of time.

Finally, you will object: A quality has a simple essence consisting in an indivisible point; therefore, according to its essence, it cannot terminate motion, which is divisible, but only change. It can terminate motion only by reason of some degree according to more or less, which does not pertain to alteration as such but to intensification or remission.

The premise is clear, because a quality has a species made stable by genus and specific difference, which is changed by any addition or subtraction; therefore it consists in an indivisible point.

We reply that, as St. Thomas says in Summa Theologiae I–II, q. 52, a. 1, a quality or form can be considered in two ways: first, in itself; second, in relation to a subject—not because in reality a form exists without a subject, but because the form is considered differently, either in itself absolutely or comparatively in relation to the subject. In the first way its species and essence are said to be indivisible; in the second, it has divisibility, by reason of which it can come to be through motion. This is readily understood with respect to intensification and remission, which, as we shall say in the next question, belong to qualities by comparison with their subjects. With respect to the quality itself as acquired absolutely and entitatively, however, the stated difficulty seems to arise: how can a form indivisible in its species and essence be acquired through divisible motion?

We reply, then, that when the species of something essentially implies contrariety and a range or distance with respect to an opposite, although it formally consists in an indivisible point insofar as all essential predicates belong to it and nothing can be added or removed in this mode of belonging, it nevertheless, comparatively with respect to its opposite term, grounds and admits a range and passage not only from privation to form but also from one form to another. This is shown by the fact that through the addition or mixture of one form with another, the species varies and some intermediate form, or several intermediate forms, results, constituting a range and distance between the extremes. Thus, by reason of this, a quality is indivisible in its formal character of constituting its species and essence absolutely, but with respect to its opposite it has a divisible mode of acquisition. And because this opposition and contrariety is exercised between forms by comparison with a subject, the statement of St. Thomas is still preserved with respect to the acquisition of quality through alteration: quality is indivisible in itself absolutely, but divisible by comparison with a subject, insofar as contrariety is exercised in that subject.

Regarding the second point, namely, how many kinds of alteration there are, we reply that alteration is a generic motion divided into three species of alterative motion: simple alteration, intensification, and remission.

Simple alteration regards the very substance of the quality as acquired through motion, namely, from some positive contrary. Intensification regards an increase of the quality by a greater or more perfect degree; remission regards its decrease by a more imperfect degree. This is because a quality has a threefold mode of range and distance: one can consider a range between different species of quality or within the same species. Between different species, as between heat and cold or other contrary qualities, a process from one to another grounds the motion of simple alteration. Within the same species, however, the same quality is present in a subject to a greater or lesser degree, which constitutes different degrees and a range according to more or less. Therefore a different motion is grounded by proceeding from a lesser to a greater degree through increase, and from a greater to a lesser through decrease; the first is called intensification, the second remission.

If there are other species of alteration, such as mixture, condensation, rarefaction, and the like, one must observe that these are not species dividing alteration according to the formality of motion—that is, according to a different mode of range and distance—but according to a specification taken from the terminating term. Condensation, for example, produces density; rarefaction, rarity; and mixture, a tempered quality. These differ from one another just as heating and cooling, and other alterations, differ according to the different terms by which they are specified. But since mixture, condensation, and rarefaction are more common and involve a more particular difficulty, they are treated especially in this work.

You will say: Why is there not likewise a threefold species of motion in quantity: toward quantity itself, toward its increase, and toward its decrease; and similarly in local motion, toward place itself, ascent, and descent? If one says that place is always acquired under some mode of position, whether straight, circular, or curved, and therefore there is no motion toward place separately, the objection is that quality too is never acquired except under some degree, whether intense or remiss. Therefore a distinct motion toward quality and toward its intensification or remission is likewise unnecessary.

This is confirmed because we find in qualities other motions besides these three, namely, motion by which a quality is extended through different parts in bodily qualities, or toward different objects in some habits. Therefore this division is not adequate.

We reply that quantity and quality are different. First, quantity does not have contrary parts between which there can be a motion from one to another, because its species are line, surface, and body, between which there is neither contrariety nor motion from one to another; indeed, all are per se required in every part of the continuum. Also, when quantity is first produced, it follows upon matter or bodily substance by way of emanation; but when, with some quantity already presupposed, another part is added or removed, this is already increase or decrease, and thus there is no place for motion toward quantity as such. Finally, every physical motion presupposes quantity, since it occurs through contact and divisibility; therefore it presupposes a divisible and tangible subject, which implies quantity.

The same is said of place: the reason is different, because within the same place there is no range or distance such that something is more or less in its local position, since a place is proportionate to what occupies it. Thus, unless the thing placed grows or shrinks, the place does not grow; but increase or decrease of what is placed does not per se pertain to local motion as it acquires that place. Therefore a range and distance is found only between one place and another, that is, between different places. In quality, however, a range is found not only between two contrary qualities, but within the same quality there can also be a greater or lesser degree. Thus there must be a motion of intensification and remission within the same quality, and simple alteration between different qualities.

To the confirmation, we reply that the motion by which a quality is extended through a subject is not a motion distinct from one of those already mentioned. Since this extension occurs through multiplication or production of a like quality, not through passage from one subject to another, extension of the quality to a distinct part of the subject is just as if it occurred from one contrary to another: it is alteration, which is motion. If it occurs from privation to form, it is generation of an accident by way of change. But when a quality is extended to new objects, as happens in habits, there is a different difficulty in reaching one inadequate object than another. This does not occur through physical alteration strictly so called, which we are now treating, but is alteration in a broad sense: it occurs through intentional or appetitive action, insofar as, on the part of the habit itself, and not only on the part of the operator or application of matter, there is a distinct perfection in reaching one object rather than another. In the opinion of some, this does not occur according to a perfection of the same quality, but through formal addition and adgeneration of a partial habit to a preexisting habit. In that case the difficulty is no different from extension of this quality through different parts of a continuum. In either case a new part of the quality is produced, although extension of habits concerns different inadequate objects, for example, different conclusions within the same science. In the view of St. Thomas in Summa Theologiae I–II, q. 54, a. 4, which we explained in Logic, q. 27, at the end,¹⁵ this extension does not involve a new formal addition through production of a new entity and quality. Rather, it is a virtual addition, insofar as the same quality or habit under the same formal aspect is more fully unfolded and extended to an object to which it did not extend before. This is to acquire a new mode of perfection, not a new entity. Therefore, since such motion is not alteration properly so called, it is no wonder that it does not constitute a distinct species, but is reduced to intensification, although it is not intensification according to more or less in the same thing, but according to extension of the same quality over inadequate objects.

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.

The unity of alteration can be considered either under the character of a change, insofar as it destroys one terminus and produces another, or under the character of motion, which includes both changes: that is, whether there is one motion or one or more changes. Continuity in alteration can be considered in three ways: first, with respect to the subject in which it exists, namely, insofar as a quality is spread through continuous parts of a subject; second, with respect to time, insofar as the alteration is contained without any interruption in duration; third, on the part of the form, namely, insofar as the form is not introduced wholly and indivisibly only in an instant, but some of it continuously over time and some of it in an instant.

On the unity of alteration.

I say, then, first: Alteration, as a motion, is one, but it includes two changes: one that corrupts the terminus from which, the other that acquires the terminus toward which.

That these two changes occur is clear from what we said above when treating generation and corruption,¹ which involve these two changes, and in q. 14 of the Physics, art. 2,² where we showed that these changes are necessary for motion, because in motion there is a transition from something to something, and consequently one thing is acquired and another corrupted. That the motion is one is clear, because it is one transition and way from subject to subject, that is, from one positive terminus to another positive terminus, between which there is a range and distance or contrariety. This range is one when there are only two termini between which the motion takes place. Such a range is found in alteration, since it is a transition from one contrary to another; therefore, there is one motion. For the same reason there is one action, because there is one agent and one patient, and consequently one procession of causality.

But you will say: Why do substantial generation and corruption likewise, being two changes, not make one motion as they do in qualities?

It is answered that changes do not produce motion unless some positive distance or contrariety to be overcome is grounded between the positive termini themselves, and not merely a being or nonbeing to be changed. The reason is that in a change, precisely as a change, only the acquisition of some being anew is intended; consequently, on the side of the terminus from which, it per se requires only nonbeing or privation. If this privation is joined to some positive form, that is incidental to such a change, insofar, namely, as the privation is found joined to some form. But in motion, not only is acquiring being anew intended; a distance between the termini over which it occurs must also be overcome, and these termini must be positive. For there is no range between the privative and the positive, since they are opposed without a middle as being and nonbeing; and if anything is found in between, it is by reason of some presupposed positive thing. Contraries, however, have a middle through which they are positively distant and opposed. Hence, since no range of contrariety such as is found in qualities is considered between substantial forms—because from participation in substantial forms as extremes no middle is participated in or tempered, nor is there a more or less in one and the same form—there is no distance and contrariety between substantial forms that grounds motion, as there is between qualities.

Secondly, you will object against the conclusion: For it follows from it that intensification and remission are not two motions, although in art. 1 we said that they are two species of motion.

The consequence is proved as follows: When there is motion from heat of degree one to heat of degree seven, there is an intensification of the heat that is acquired and a remission of the cold that is lost; as much cold is lost as heat is acquired. Therefore, that change of the cold is a remission, and yet there is only one motion, since there is only one way and one terminus acquired and one lost. Otherwise, whenever a quality is intensified there would be two motions: one from less heat to more, the other a remission of cold from more to less.

It is answered that intensification and remission are in themselves distinct motions, like increase and decrease, ascent and descent. They are contrary when they concern the same form, for example, intensifying or lessening heat. When they concern different forms, for example, intensifying heat and lessening cold, these motions are either disparate, if the forms themselves have no order and connection with one another, or coordinated, if the forms themselves are successive in relation to one another, so that one lessens or expels the other. However, when a motion of intensification is found that corrupts or attenuates cold, it is not per se a motion of remission, because it is not per se a lessening, but follows as a consequence insofar as it is the corruption of the cold present in the subject. Yet because this is incidental with respect to the intensification of heat, that motion is not called a remission, nor does it occur in the manner of a motion, but in the manner of a change that corrupts some of the cold consequentially and incidentally, as heat is intensified. Motion does not take its species, nor is it constituted as motion, according to what is incidental and consequential, but according to what is per se and on the side of the terminus toward which; it does not take it merely from the side of the terminus from which. Therefore, when heat is intensified, although there is a lessening of cold, there is not a motion of remission, because that lessening of cold belongs precisely to the side of the terminus from which, as the terminus that is changed and destroyed and stands in succession to the acquisition of heat; it is not a motion per se that lessens, whose terminus toward which would be the lessening of cold. Thus it is not per se a motion of remission, but a change that destroys cold, not one that per se lessens and tempers it. Sometimes, however, intensification can occur without the remission of its opposite, as in the intensification of light, which already presupposes that darkness has been expelled, and in the intensification of charity, which presupposes that sin has been expelled through charity's first introduction. Hence intensification is not always joined to a remission, even as a change that occurs incidentally.

On the continuity of alteration.

I say, secondly: Alteration that is truly motion is continuous, as opposed to discrete, if we attend to the continuity that occurs through the extension of a quality in the parts of a continuum, whether through the duration of time or through the intensification of the form.

We say “as opposed to discrete motion” because if we take “continuous” to mean perpetual and without ceasing, then alteration is not continuous in that sense, but very often ends and is interrupted. Thus, although a quality can be produced in an instant, as when the final disposition is formed, nevertheless, when it occurs through true motion, it occurs neither in an instant nor through many instantaneous actions, such that nothing of the quality is produced between one instant and another and there is only a disposition for production to occur in an instant, as some have thought. The opposite view, however, is commonly held, as can be seen in Magister Báñez on Book 1 of On Generation, ch. 4, q. 6, “On Alteration”; in the Carmelite Course, disp. 2, “On Alteration,” q. 10; in the Coimbra commentary on Book 1 of On Generation, ch. 4, q. 2, art. 2; and by others.

We must therefore prove two things: first, that alteration cannot occur in an instant, but has succession in temporal duration; second, that in the extension or intensification of a quality, something of the quality is produced not only at instants but also in the intervening time between one instant and another, and that the altering action does not cease.

The first was proved by us in q. 21 of the Physics, art. 2,³ because successive motion does not exist in an instant, since, precisely insofar as it is successive, it is not indivisible. For every succession implies one part after another; therefore, it implies divisibility and thus does not coexist with, or receive its measure from, instantaneous duration.

This also follows from the teaching of Saint Thomas, Summa theologiae I, q. 53, art. 3, as we also adduced there: it cannot be the case that some subject rests under one form for the whole of a period of time and, in the final instant of that period, is under another form, as though it had been changed into it in the completed state. Therefore, motion can never be completed in a single instant, so that before that instant there is none of the motion and in the final instant there is the motion and its terminus, that is, the having-been-moved. For there cannot be a having-been-moved unless some being-moved precedes it, that is, some tendency to acquire that form and expel the opposite form. But for the subject to rest throughout the preceding period, it must be under one form in such a way that it is neither on the way to that form's corruption nor tending toward another, but is in the same state now as before. Therefore, it cannot be the case that something is changed in the final instant while no being-moved precedes it throughout the period, but only rest.

This is also apparent in instantaneous changes, if they occur according to the order and manner of nature. Some motion precedes, either by way of disposition or by way of application, as is clear in substantial generation and illumination. For substantial generation depends on a preceding alteration, which is motion. Similarly, a luminous body does not naturally illuminate a space where it did not illuminate before unless it is newly produced there or newly brought there. If it is newly brought there, local motion precedes; if it is newly produced there through natural generation, as when fire is made, alteration precedes. Thus, in the natural order, nothing is ever placed under a new form, even instantaneously, unless some motion precedes. If, however, by divine power something is produced or created suddenly without any preceding disposition or motion, that does not belong to the natural manner of operation of which we are speaking here. So too it is no wonder that Christ's body is placed under the species of bread at some instant, although no motion toward it preceded, because this occurs by supernatural power, not in the natural way. For this reason, Saint Thomas, at the cited place, proves that an angel cannot move in an instant while resting in another place throughout the preceding time. If an angel exists in another place throughout a complete instant, without any time or motion, at rest, then the instant of its existence in one place must differ from the instant of its existence in another, so that it rests in one place not throughout a period of time but throughout an instant, and in another instant is in another place. But then the departure from one place, which occurs in an instant through the final state of being, and the beginning of another, which occurs in another instant, are measured not by one instant but by two. Thus that discrete motion occurs not in an instant but in instants. Hence motion, even discrete motion, is never verified in a single instant.

The second point to be proved in this conclusion is that, if motion is continuous with a continuity belonging to the form, in this sense: if some of the form is produced in an instant, some of it is also acquired in time, and the action and continuation of the form do not cease between one instant and another. Some deny this part. Yet it follows from Saint Thomas in II Sentences, dist. 5, q. 2, art. 1,⁴ where he proves that the dispositions for substantial generation precede the introduction of the form in time, because alteration is continuous motion, and therefore its beginning and middle precede the introduction of the form. Hence alteration occurs in time and is not discrete across instants. The holy Doctor posits the same continuity of alteration through the intermediate time between two instants in Quodlibet 9, art. 9.⁵ It can also be seen in his commentary on Book 1 of On Generation, lect. 24,⁶ on text 84,⁷ and in his commentary on Book 5 of the Physics, lect. 7.⁸ It is taken from the Philosopher in the same Book 5 of the Physics, text 39,⁹ where he says “that every motion is continuous, and that it must be one and continuous simply.”

The reason is this: Either some motion continues between two instants, so that the action does not cease and the subject does not rest, or all motion and the action producing the quality cease between one instant and another. If the first, then that motion and flux between instants cannot be understood without some flowing form, which in an instant has a having-been-moved, or exists in the completed state, while in time, that is, in motion, it exists in a process of becoming and being moved; for motion is not something apart from the things toward which it is motion. Thus, if motion really occurs between one instant and another, a form really exists, being identified with that motion as with a flowing terminus that successively passes from nonbeing to being. If the second is asserted, it is impossible: if a quality is produced in this instant and the motion ceases immediately afterward, while something is produced in the next instant, that thing will not have been acquired through motion or alteration, which is motion, but through another action distinct from succession and motion, and no such action is apparent. Moreover, between one instant and another the agent is duly applied so as to act, and the patient is capable of receiving and is unimpeded, no less than in the following instant; for, as we assume, the patient has not changed from its disposition between instants, nor the agent from its activity. How, then, is the agent suspended from acting between instants? Finally, in local motion one does not cease moving between instants, because one gradually passes from one place to another through the middle and overcomes the distance between two places. Therefore, similarly, the distance and contrariety between qualities and their degrees of intensity must be overcome through the succession and continuation of motion, by producing something between instants.

Nor can it be said that between instants the agent produces something, but not the form, for example heat, rather some disposition toward heat, such as rarefaction or the like. For besides the fact that there is no disposition toward heat, since heat itself is a first quality, even if this were granted, the same argument applies to that disposition. Either it is a quality or it is not. If it is not a quality, one cannot specify what it is or to which category it belongs; or, if it is a mode of the same quality, what mode is it besides intensification and remission? For if these are produced in time, then the motion of intensification is continuous. But if that disposition is a quality, for example rarefaction, then some quality is already produced between instants, and consequently the same reasoning applies to heat itself.

You will say: Although motion is continuous in the intensification of a quality and something is produced between instants, nevertheless, when the alteration is from one quality to another, for example from white to black, what quality is produced between instants, since the intermediate quality is not produced divisibly but indivisibly? For it is a true species of quality, having indivisible being and terminating the having-been-moved. It is answered that when one passes from white to black through an intermediate quality, for example pale, then between instants pallor occurs imperfectly, insofar as whiteness begins to fade and fall away from its perfection: whiteness is in the process of being corrupted, which is pallor in the process of becoming. This occurs between instants because that corruption of whiteness and acquisition of pallor have a range; thus, a part of that range occurs in time and is completed in the completed state at some instant.

On the indivisibles of alteration.

Since a continuum consists of connected parts, which are joined by certain indivisibles, it is necessary to explain how these indivisibles occur in qualities and in successive alteration.

It is answered that the indivisibles of a quality must be considered according to its different modes of indivisibility. For one finds divisibility of extension by reason of the subject's quantity, divisibility of motion by reason of succession, and finally divisibility of form according to more and less in intensification and remission.

As to the first, just as accidents have quantitative extension through quantity, which affects substance and extends it and the accidents in it, so through quantity a quality is made extended and divisible; consequently, through quantity it will also have indivisibles that connect this quantitative divisibility. And just as substance has neither divisibility nor indivisibles except through quantity, as was proved in Book 6 of the Physics, q. 20,¹⁰ and in q. 16 of the Logic,¹¹ so neither do quality and other materially extended accidents have indivisibles of this extension except through quantity; for in this respect the same reasoning applies to them and to substance.

As to the second, we say that in alteration, insofar as it is motion, there are indivisibles as in other motions: namely, the indivisibles are the very having-been-moved states in the succession of the quality, which terminate or connect the succession of motion itself, as we explained in q. 20 of the Physics, art. 1.¹² This having-been-moved, as is drawn from Saint Thomas, Summa theologiae I, q. 53, art. 3, is explained by the fact that the mobile is not in the same disposition at every instant of the time in which it is moved. Thus, insofar as that disposition is in the process of becoming, it is said to be in the process of being moved; insofar as it is terminatively in the completed state, it is said to have been moved, and then the disposition is different. Accordingly, whether this having-been-moved consists in some indivisible in which it is completed and terminated, or in some other mode or respect, that which formally constitutes the having-been-moved is what constitutes the mobile in one disposition after another terminatively and in the completed state: all the parts that are in the process of becoming through time are in the completed state at an instant, and from that completed state follows another process of becoming of another part, which is in the completed state at another instant, continuing up to the final instant at which it stops. Thus a quality, by successively inducing different having-been-moved states, constitutes different successive indivisibles of the motion of alteration.

As to the third, namely the indivisibles of the quality or form itself that is acquired through alteration, a difficulty can arise within the same quality, when it is intensified or lessened: must this divisible range of intensification or remission connect and join its parts through certain indivisibles? This pertains to the following question, where we will treat the intensification and remission of qualities.

A difficulty can also arise as to whether, in the very range or distance found between two contrary qualities, through which the transition from one to the other takes place (as pale, green, blue, and so forth are posited between white and black), indivisibles must also be posited by which this divisible range and distance is joined together. Yet in this there appears to be no reason to posit indivisibles, because these species are not continuous with one another, nor do they have parts of the same nature that need to be joined by different indivisibles; for they are different colors or other intermediate qualities. Within the species of color there is a range from an imperfect and incipient color to another perfect intermediate color, and from that to another, up to the extreme, with the corruption of the prior color, which is expelled. Then no indivisible is acquired to join the parts, but rather a certain determinate species. Yet because it is intermediate and imperfect, it prepares the way and transition to another, which arises from the tempering and mean of the other; therefore it forms a range to be overcome by motion, not one to be joined by indivisibles.

The arguments are solved.

First you will object against the continuity of alteration: The motion of alteration in intensification cannot be continuous; therefore, the conclusion, which speaks of every alteration, is false. The antecedent is proved: What is produced through such a motion is some mode of ever-greater rootedness in the subject. But such modes are indivisible in themselves, as will be proved in the following question; therefore, they cannot terminate motion, since terminating it requires some divisibility and range in the terminus, so that a part of the terminus corresponds to a part of the motion, and an indivisible terminus to an indivisible motion.

It is confirmed, because every part of the motion truly and properly produces something. Therefore, something in the terminus of the motion must correspond to every part of the motion itself, and thus the terminus must have prior and posterior parts. Therefore, if every degree is something indivisible, at least formally the whole degree is produced by the first part of the motion, and nothing will be left for another part or the middle to produce.

It is answered that there is no contradiction in the parts of motion terminating at something indivisible, insofar as it is the terminus of the parts, just as the parts of a line terminate at an indivisible point. Similarly, in motion all the parts of motion terminate at the very having-been-moved, because all the parts of motion are in the process of becoming with respect to it. Indeed, every terminus must be indivisible and terminate divisible parts, not by inhering in each one singly and adequately, but inadequately in some indeterminate one, as we said in q. 20 of the Physics, art. 2,¹³ and thus, although it is not adequate to them informatively, it is adequate to them terminatively, since it is the terminus of them all. Thus, in a quality when it is intensified, some degree or terminus is acquired through motion. Although it is indivisible in itself, as a terminus, it nevertheless implies divisibility virtually, insofar as it presupposes parts and is their terminus. Therefore, divisibility is not required in the terminus in itself and formally, but by reason of the parts it terminates and that must be acquired successively through motion.

To the confirmation, it is answered that every part of motion produces something, namely that having-been-moved, but not every part of motion produces it adequately. Although that terminus is indivisible in itself, it terminates several things that can stand under it and regard it as their completed state. If it had prior and posterior parts, it would not be their terminus but their equal.¹⁴ Nor does the first part of motion produce the entire indivisible, or having-been-moved: both because there is no first part of motion there, where all the parts are indeterminate and confused, and because that middle portion produces the terminus inadequately, that is, as a partial becoming of it, not as its entire becoming.

Secondly, it is argued: In alteration and intensification there is not only one terminus, but several, which are acquired as the same action continues; therefore, there cannot be one motion, because there is not one terminus from which its unity can be taken. The antecedent is clear, because while the motion of alteration continues, several termini are produced, for example, several degrees in intensification or several intermediate qualities in alteration from one species to another. Therefore, the terminus is not one, and consequently neither is the motion; thus it will not be continuous.

It is confirmed: If alteration were continuous motion and lasted, for example, an hour, then at the end of the hour an infinite quality would have been produced, because there are infinitely many instants and consequently infinitely many having-been-moved states. Therefore, if intensification occurs throughout that hour, those infinitely many are attained, each of which increases the intensity and degree; consequently, at the end of the hour the quality would become infinite.

It is answered that in continuous alteration there is one adequate terminus, although there are several inadequate termini. The adequate terminus has unity by reason of the last terminus at which the motion stops and to which the others are ordered. So too, in local motion, when several places are reached up to the last, the unity of that continuous motion is taken from that last place; and therefore it is one simply, because it terminates simply in one, as we explained more fully in q. 19 of the Physics.¹⁵ Thus, at any instant a different inadequate place can be acquired. Between one instant and another, however, there is a transition from place to place, and then one is said to be in a place as in the process of changing, not in the having-been-moved, about which we spoke more fully there.

To the confirmation, it is answered first that the argument proceeds even if alteration is discrete motion, because just as within an hour there are infinitely many divisible parts, so there are infinitely many indivisible instants, in the same way as there are infinitely many parts. Therefore, although there is no motion or action between instants, the same difficulty remains: how does that intensification of the quality occur in the infinitely many instants contained within an hour, without becoming infinite? The answer, then, is that this infinity of instants and of the infinitely many parts contained in every continuum is potential infinity, not actual infinity, because it is an infinity contained and exhausted in aliquot and finite parts; therefore it is finite in actuality and only infinite potentially, as we showed more fully in q. 15¹⁶ and q. 20 of the Physics.¹⁷ For something to be actually infinite, it must consist of infinitely many aliquot parts, since those parts must be equal to a third thing and must not overlap one another. But those infinitely many parts are proportional, indeterminate, and overlapping one another, as we explained in the cited places. Instants, or indivisibles, are related in the same way: they multiply in the continuum together with the parts themselves and in the same manner. Hence they yield only potential infinity, that is, because the divisibility of the whole can be designated infinitely from any part; and so from the fact that intensification lasts for the whole hour it follows only that the quality has infinitely many potential parts and, similarly, indivisibles, but finitely many in actuality, since they are contained within the finite bounds of an hour.

Third, it is argued: If alteration is continuous motion, it cannot begin through a first being, but must begin through a last nonbeing, as other motions do; but this is impossible. Therefore, the conclusion follows.

The minor is proved as follows: If it begins through a last nonbeing, it is true to say, “Now the agent is not altering; immediately afterward it will alter.” At that “now,” then, either the agent is duly applied to the patient, in which case there is no reason it would not act once that application is posited; or it is not duly applied, in which case it will not act immediately afterward either, because the whole application cannot be completed immediately afterward, since it is divisible, being made through motion and in a divisible part. Thus, immediately afterward it will not be wholly applied in the completed state, and therefore the action will not follow. It is likewise unreasonable that a quality, which is a permanent thing, should not begin through a first being, especially since it is a determinate disposition in which a minimum must be assigned, and consequently something definite and determinate; therefore it must begin through a first being. Finally, it is confirmed that this seems to be Aristotle's intention in Book 8 of the Physics, text 23,¹⁸ where he says that “to say that the continuous is altered is to oppose the evident facts,” and adds that “alteration does not occur part by part like freezing, but suddenly, as when a stone is excavated by the last drop”—something that is evidently not continuous motion. Saint Thomas affirms the same in his commentary on the same place, lect. 5,¹⁹ in his commentary on Book 6 of the Physics, lect. 5,²⁰ in Summa contra Gentiles II, ch. 49, and elsewhere.

It is answered that without doubt alteration, like other motions, and the quality produced through it, begins through a last nonbeing. In reply to the proof, it is said that whether the agent's application to motion occurs in an instant or not, its being actually applied belongs to the having-been-moved and is in an instant. Yet it does not begin intrinsically in that instant, and so the inference does not properly follow: “The agent is actually applied in this instant; therefore, action or motion is intrinsically in this instant.” For it does not follow that the action is intrinsically in this instant unless the action itself is instantaneous; it is enough that it begin extrinsically, because it will occur immediately afterward. Therefore, motion need not follow upon the very being-applied except according to its nature: if something is applied in an instant, motion is not intrinsically given in that instant but immediately afterward, and thus it begins extrinsically in that instant, just as a heavy body, when generated upward, begins to move in that same instant not intrinsically but extrinsically. In fact, however, there is no first being-applied, just as there is no first having-been-moved in motion; for application is made through motion.

As to the claim that a quality is a permanent thing and therefore must begin through a first being, I distinguish. It is a permanent thing when it exists determinately in the completed state: I grant this; when it is in flux and becoming: I deny it. Or, secondly: that it is a permanent thing beginning in a permanent manner: I deny; beginning in a flowing and successive manner, after the manner of motion: I grant. In that case it conforms to its manner of coming to be, which is through motion, not to its proper manner of being, which it has in the completed state. A quality that is a disposition toward a substantial form, however, must express something determinate under that state of disposition, especially when speaking of the ultimate disposition. For other dispositions can have a range and indivisibility; that one, then, will begin in an instant, not in the manner of motion.

To the confirmation, it is answered that in the cited places Aristotle and Saint Thomas intend only to argue against certain ancient philosophers who held that everything is always moving and never at rest: alteration is not continuous motion, that is, it does not last perpetually, though this does not mean that it is discrete for as long as it lasts. When he says that alteration does not occur part by part but suddenly, this is understood of alteration with respect to its final effect and disposition, not of alteration absolutely and in itself.