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.