Aquinas on Change Without Matter or Form— The Problem of Local Motion

1.1 Change and the Aristotelian Categories

Aquinas’s views on change are closely connected to his understanding of the ten Aristotelian categories. In particular, Aquinas allows for changes in each category, and hence for ten general types of change—one substantial and nine accidental. Like Aristotle himself, moreover, Aquinas often uses examples of qualitative change to illustrate the nature of change in general. Here are two of his favorite examples:

Paradigm Examples of Change

• Change of shape: Some bronze goes from being lump-shaped to statue-shaped, as a result of the activity of some artisan.

• Change of temperature: Some water goes from being cold to hot, as a result of being placed over a fire.⁸

Aquinas thinks of shape and heat as paradigm examples of qualities, which he takes to be forms (formae) of a certain type—namely, accidental forms inhering in substances.⁹ Given that Aquinas takes form and matter to be correlative notions, it is not surprising that his reliance on such examples would suggest that change in general can be understood in terms of the reception of form by matter.

Although Aquinas thinks that there can be as many types of change as there are Aristotelian categories, he typically follows Aristotle in focusing on just four types—namely, those associated with the categories of substance, quality, quantity, and spatial location or “where” (ubi).¹⁰ Indeed, like Aristotle, Aquinas takes these four to be the only primary or “per se” types of change, and he introduces special names for each:

Types of Per Se Change

In describing these four types of change as per se, Aquinas means to contrast them with the types of change associated with the other six categories, which he describes as per accidens. We can gather what Aquinas has in mind by this distinction from what he says about changes associated with the specific category of relation:

There is no per se change in [the category of] relation, but only change per accidens; for a new relation follows on another change (e.g., a change of quantity in the case of [relations of] equality or inequality, and a change of quality in the case of [relations of] similarity or dissimilarity). (In V Phys., lect. 3, n. 7)

Here, Aquinas suggests that whether a given type of change qualifies as per se or per accidens depends on whether it “follows on” (sequitur) another change. Judging by the examples he uses to illustrate such “following,” he appears to have in mind a distinction between those changes grounded in other changes, and those not so grounded. Thus, changes associated with the category of relation qualify as per accidens, rather than per se, precisely because they are grounded in changes associated with other categories (e.g., quantity or quality). With this understanding it is easy to see why Aquinas would focus only on per se types of change. For they are the metaphysically fundamental ones, in terms of which all other types of change must be understood.

It is important to note that, in addition to describing local motion as a change of spatial location (ubi), Aquinas also describes it as a change of place (locus). This is because he thinks that spatial location itself “consists in a kind of relation to place” (consistit in aliquali relatione ad locus).¹¹ What is more, Aquinas follows Aristotle in conceiving of individual places as containers (continentia) or receptacles (receptacula) for bodies located at them.¹² As Aquinas recognizes, on this conception it is natural to think of places as regions of space (spatium). But here again he prefers to follow Aristotle in thinking of them as surfaces or boundaries of surrounding bodies. The details of Aquinas’s specific conception of place are complicated and difficult to understand. Fortunately, though, none of the conclusions I draw in what follows depends on them. For our purposes, it will be enough to appreciate that Aquinas takes places to be entities of some type or other, which can be filled by different bodies at different times.

One final point: although Aquinas is happy to describe spatial location as “a kind of relation”—namely, one that a body bears to a place—it is also important to note that, strictly speaking, he does not take spatial location to fall within the Aristotelian category of relation (relatio, relative, ad aliud). The same is true of inherence (inhaerentia), which is the relation a form bears to the substratum possessing it. The reason is that, like other medieval philosophers, Aquinas identifies categorial relations only with those that both (a) hold between distinct substances, and (b) are grounded in intrinsic features of their relata. Thus, equality and similarity count as categorial relations because they both hold between equal or similar substances, and are also grounded in quantities or qualities of those same substances (the so-called fundamenta of their relations). Neither inherence nor spatial location, by contrast, count as categorial relations; for inherence is not a relation holding between distinct substances, and spatial location is not grounded in intrinsic features of its relata. Although I shall continue to refer to both inherence and spatial location as relations, I wish to emphasize that I do not mean thereby to suggest that they count as relations in Aquinas’s categorial sense.¹³

So much for the categorial framework in terms of which Aquinas develops his theory of change. Let us now turn to the details of the theory itself.

1.2 Three General Principles of Change

In what follows, I present Aquinas’s theory of change in terms of six principles. In the remainder of this section, I focus on the first three principles, which connect Aquinas’s views about change to potentiality (potentia) and actuality (actus).¹⁴ In the next section, I turn to three further principles, which connect these same views to matter (materia) and form (forma).

There is no single word in Latin corresponding to our English word ‘change’. When Aquinas wishes to characterize change in general, therefore, he relies on the Latin terms ‘mutatio’ and ‘motus’. Aquinas often uses these terms in a narrow sense to mark different species of change, with motus corresponding to gradual change and mutatio corresponding to instantaneous change.¹⁵ But he also uses both terms in a broad sense to cover any type of change, as in the following passage:

In every change or motion (mutatio vel motus), there must be something that exists in a different state now than it did previously (aliter se habens nunc et prius). Indeed, this is implied by the very meaning of ‘change’ (mutatio). (SCG II, cap. 17, n. 4)

As this passage suggests, Aquinas conceives of change in the same basic way that philosophers now usually do—that is, in terms of a subject’s existing in different states at different times.¹⁶ Thus, if some bronze undergoes a change of shape, it must exist “in a different state now than it did previously”—say, that of being statue-shaped instead of lump-shaped. Likewise, if some water undergoes a change in temperature, it too must exist in different states at different times—say, that of being hot at one time, cold at another. And, of course, the point is not restricted to changes of these two types alone, but applies to “every change or motion.”

It is natural to suppose that when a subject comes to exist in new state (i.e., one in which it did not exist previously), it does so in virtue of acquiring some new form or property. That is, it is natural to suppose that states of change can themselves be analyzed in terms of the possession of distinct forms or properties by subjects. We have already seen that Aquinas holds something like this view in the case of changes involving qualitative states. For when a subject comes to be statue-shaped or hot, Aquinas thinks it does so in virtue of acquiring a quality, which he takes to be a form. It is important to emphasize, though, that nothing in Aquinas’s characterization of change in general requires this sort of analysis. Indeed, the Latin phrase I have translated as “existing in a different state now than it did previously” (aliter se habere nunc et prius) literally means “holding itself differently now than it did previously.” But even someone who denies the existence of forms or properties altogether can allow that things undergo change, and hence “hold themselves differently” at different times. As all of this makes clear, talk of “states” in the context of Aquinas’s characterization of change is meant to capture our intuitive sense of the different ways that a changing thing exists at different times, and not to take a stand on the precise ontological commitments of these “ways of existing.”

For Aquinas, then, all change involves coming-to-be (fieri)—or more precisely, a subject’s coming to exist in a new state. But we should note here that Aquinas does not think of all coming-to-be as involving change. For he takes creation (creatio) to be a type of coming-to-be distinct from change:

Creation does not qualify as change—unless it is merely according to certain mode of understanding. For it is part of the concept of change (de ratione mutationis) that one and the same thing exists in a different state now than it did previously … But in creation, which involves the production of the whole substance of things, it is not possible for one and the same thing to exist in a different state now than it did previously—unless it is merely in our understanding (e.g., if we conceive of something as completely lacking existence at one time, and afterwards possessing it). (ST Ia, q. 45, a. 2 ad 2)

As this passage indicates, Aquinas takes change and creation to involve different types of coming-to-be. Change involves what we might call qualified coming-to-be—that is, a pre-existing subject that merely comes to exist in a new state. Creation, by contrast, involves what we might call unqualified coming-to-be—that is, a subject that comes into existence for the first time as a result of being produced ex nihilo. Aquinas recognizes that it might be tempting to think of creation along the lines of change—that is, as if it involved a subject going from a state of not existing to existing. But as he suggests, we shouldn’t take this way of thinking to have any real basis outside the mind—presumably because there are no non-existent objects.¹⁷

As Aquinas sees it, the distinction between change and creation carries with it a distinction between different types of potentiality, actuality, and efficient causation. For change to occur, there must not only be a pre-existing subject, but also what Aquinas calls a passive potentiality (potentia passiva)—a potentiality of some pre-existing subject to undergo the change in question. For the same reason, Aquinas thinks, the actualization of such a potentiality requires an efficient cause or agent to act on the pre-existing subject (or patient), in such a way as to produce in it a new state.¹⁸ Things are very different in creation, of course. Insofar as creation involves unqualified coming-to-be, there can be no pre-existing subject, much less a passive potentiality of such a subject to be created. Indeed, it is precisely for this reason that Aquinas describes creation as “the production of the whole substance of things.” Aquinas recognizes that it might be tempting to think of creation as if it involved the actualization of a passive potentiality. After all, if something is created, it must be “creatable.” But here again, Aquinas warns against taking these ways of thinking too literally:

Something is said to be creatable, not through any passive potentiality, but only through the active power (per potentiam activam) of the creator, who is capable of producing something ex nihilo. (ST Ia, q. 75, a. 6 ad 2)

As Aquinas here suggests, talk of potentiality in the context of creation must be understood in terms of active rather than passive potentiality—that is, in terms of some agent’s power to create rather than in terms of some pre-existing subject’s passive potentiality to be created.

We are now in a position to articulate the first three principles governing Aquinas’s theory of change:

Theory of Change I: General Principles

1. (P1)

1. Change and qualified coming-to-be. For a change to occur just is for a pre-existing subject to come to exist in a new state (i.e., one in which it did not exist previously).

1. (P2)

1. Change and the actualization of passive potentiality. For a pre-existing subject to come to exist in a new state just is for its passive potentiality for existing in that state to be actualized.

1. (P3)

1. Change and efficient causation. A pre-existing subject’s passive potentiality for existing in a new state cannot be actualized without some efficient cause acting on it.

I have described P1–P3 as “general principles” in order to emphasize that they are meant to apply to changes of any specific type. P1 and P2 give us an understanding of change itself—P1 analyzes change in terms of a specific type of coming-to-be, whereas P2 further analyzes the relevant type of coming-to-be in terms of actualizing a passive potentiality. P3 then connects this understanding of change to efficient causation.

So much for our first three principles. Let us now turn to three further principles, which connect Aquinas’s views about change to his hylomorphism.

1.3 Three Further Principles of Change

The first three principles governing Aquinas’s theory of change are fairly easy to understand and touch on familiar aspects of his views. The same cannot be said for the principles to be articulated in this section. For the same reason, my approach to them will be different. Rather than begin with a discussion of particular texts from which these principles emerge, I instead start with a statement of the principles themselves and then turn to the question of how they relate to Aquinas’s texts.

Here, then, is a statement of the principles:

Theory of Change II: Further Principles

1. (P4)

1. Change and the ontology of states. For a pre-existing subject to come to exist in a new state just is for that subject to come to be newly related to a distinct entity—namely, a terminus of change.

1. (P5)

1. Change and the reception of distinct forms. For a pre-existing subject’s passive potentiality for existing in a new state to be actualized just is for that subject to receive a new entity—namely, a distinct form that it previously lacked.

1. (P6)

1. Change and the production of distinct forms. A pre-existing subject’s passive potentiality for existing in a new state cannot be actualized without some efficient cause producing a new entity in it—namely, a distinct form that it previously lacked.

Although I have stated P4–P6 as perfectly general principles, eventually we shall see that there is a question about whether they really apply to all types of changes. For now, however, I want to emphasize that the key to understanding all three principles lies in an aspect of Aquinas’s views that we have not yet addressed but that is explicitly mentioned in P4—namely, the notion of a terminus of change.¹⁹

Just as Aquinas thinks that every change involves a subject that is changed, so too he thinks that every change involves some termini with respect to which its subject changes. Consider, for example, the following passage:

Five things are required for any change (motum). First, there must be a primary agent (primum movens)—that is, a source from which the change originates. Second, there must be something changeable that is [actually] changed. Third, [there must be] some time in which the change occurs. In addition to these three things, moreover, there must be two termini—one from which the change begins and another towards which it proceeds. For every change is from one thing to another. (In V Phys., lect. 1, n. 4)

Here, Aquinas identifies termini as two of five things required for any change. The other three—an agent, a changeable subject, and time—are all things that we would expect given his commitment to P1–P3. Thus, insofar as change requires efficient causation (P3), we would expect it to require an agent or “source from which the change originates.” Likewise, insofar as change requires the actualization of a passive potentiality (P2), we would also expect it to require “something changeable that is [actually] changed.” And finally, insofar as change requires a subject to come to exist in a new state (P1), we would expect it to require “some time in which the change occurs.” For evidently a subject cannot exist “in a different state now than it did previously” if it does not persist through some temporal interval.²⁰

But what about the termini? How are they related to what we have seen of Aquinas’s views about change? Initially, it might be tempting to identify the termini with the different states in which the changing subject exists at different times. For insofar as change requires a subject to come to exist in a new state (P1), it clearly requires a pair of states—indeed, “one from which the change begins and another towards which it proceeds.” What’s more, it seems perfectly natural to describe change as proceeding “from one state to another.”

Although this identification is initially tempting, for reasons to be explained shortly we must resist it. But if the termini are not states of change, what are they? To answer this question, we must turn to Aquinas’s analysis of substantial change. For it is only in the context of explaining this type of change that Aquinas makes his views about termini clear. Indeed, as will become clear, in this context Aquinas not only distinguishes termini from states of change, but also connects them to matter and form—and, along the way, gives strong evidence for his commitment to P4–P6.

Consider, therefore, the following passage, which contains what might be Aquinas’s most detailed treatment of the nature of substantial change (for ease of reference, I hereafter refer to it as ‘Passage A’ and number the lines of its text):

In this passage, Aquinas focuses on explaining the nature of the subject of substantial change, and in particular on presenting what he takes to be Aristotle’s argument for identifying that subject with a specific type of matter—namely, “prime matter.” But in the course of presenting this argument Aquinas also clarifies the relationship of substantial change to change in general. Thus, he begins (ll. 1–16) by arguing that substantial change must have both a subject and some termini, precisely because this is required of change as such. He then argues (ll. 16–26) that the subject of substantial change must be identified with matter, precisely because its termini involve form—or rather form and privation.

For the sake of clarity, we can reconstruct the argument of Passage A more precisely as follows:

Argument from Substantial Change

1. There must be both a subject and some termini for any type of change. (ll. 4–5)

2. There are substantial changes. (l. 13)

3. Hence, there must be both a subject and some termini for substantial change. (ll. 14–16)

4. The termini for substantial change are form and privation. (ll. 16–17)

5. Hence, the subject for substantial change must be (prime) matter. (ll. 20–26)

The inference from 1 and 2 to 3 is clearly valid. But the inference from 3 and 4 to 5 is enthymematic and specifically depends on Aquinas’s views about the correlativity of matter and form. In other words, it is precisely because the termini of substantial change involve some type of form that Aquinas thinks that we are entitled to infer that its subject must qualify as matter in some sense. Aquinas’s mention of “prime” matter in his statement of the final conclusion might seem to come from nowhere; I shall have more to say about its significance shortly. But first let us take a closer look at Aquinas’s understanding of the argument’s main premises and their relation to our principles P4–P6.

2.1 Principles of Local Motion

There can, I think, be little doubt that Aquinas’s views about local motion are governed by the first three principles—namely, P1–P3. For as we have seen, Aquinas thinks of local motion as change with respect to the category of spatial location (ubi) and hence as involving “a common subject that is now here and later somewhere else.” But to say that a subject exists in different spatial locations at different times is, presumably, just a way of specifying the types of state involved in local motion. Moreover, if a subject is going to change with respect to its locative states, it must not only possess the potentiality to do so, but must also at some time actualize that potentiality. Finally, just as the actualization of potentiality in general requires an efficient cause, the same is surely true for the actualization of a potentiality for a new spatial location. In short, there is no reason to doubt that Aquinas would accept each of the following specifications of P1–P3:

Theory of Local Motion I: General Principles of Change Specified

1. (P1_L)

1. Local motion and qualified coming-to-be. For a local motion to occur just is for a pre-existing subject to come to exist in a new locative state (i.e., one in which it did not exist previously).

1. (P2_L)

1. Local motion and the actualization of passive potentiality. For a pre-existing subject to come to exist in a new locative state just is for its passive potentiality for existing in that state to be actualized.

1. (P3_L)

1. Local motion and efficient causation. A pre-existing subject’s passive potentiality for existing in a new locative state cannot be actualized without some efficient cause acting on it.²⁴

As for the other three principles we articulated, P4–P6, it is much more difficult to see how Aquinas could accept them. More precisely, it is difficult to see how he could accept two of the three. To see why, consider the following specifications:

Theory of Local Motion II: Further Principles of Change Specified

1. (P4_L)

1. Local motion and the ontology of states. For a pre-existing subject to come to exist in a new locative state just is for that subject to come to be newly related to a distinct entity—namely, a terminus of local motion.²⁵

1. (P5_L)

1. Local motion and the reception of distinct forms. For a pre-existing subject’s passive potentiality for existing in a new locative state to be actualized just is for that subject to receive a new entity—namely, a distinct form that it previously lacked.

1. (P6_L)

1. Local motion and the production of distinct forms. A pre-existing subject’s passive potentiality for existing in a new locative state cannot be actualized without some efficient cause producing a new entity in it—namely, a distinct form that it previously lacked.

Specified this way, it is not hard to see how Aquinas could be said to accept the first of these principles, P4_L. For like all other changes, he clearly takes local motion to involve both a subject and some termini. But for reasons I shall now explain, his conception of the termini for local motion makes it difficult to see how he could accept either P5_L or P6_L. For whereas other types of change can be said to involve forms precisely because their termini do, the same cannot be said of local motion:

Just as the type of change that occurs in respect of forms led human beings to a knowledge of matter (since there must be a subject in which forms can succeed one another), so too the type of change that occurs in respect of place led human beings to a knowledge of place (since there must be something where [aliquid ubi] bodies can succeed one another). And this the point that [Aristotle] makes later—namely, that when some water departs from where it now exists (e.g., a particular vessel), some air comes to replace it.

Since, therefore, distinct bodies may exist in the same place [at different times], it seems clear that place is something distinct from the things that both exist in place and are moved with respect to it. For it would not be possible for some air now to exist where some water existed previously, if place were not distinct from both the air and the water.

Consequently, place is something (aliquid); indeed, it is a type of receptacle (quoddam receptaculum) distinct from any of the objects located at it. What is more, place is the terminus from which local motion begins and toward which it proceeds. (In IV Phys., lect. 1, n. 6)

Here Aquinas distinguishes local motion from other types of change precisely because its termini must be identified with places (loci) rather than forms (formae). As I noted earlier (§1.3), Aquinas’s specific views about the nature of place are complicated, and the details need not detain us. For our purposes, it’s enough to see that when a body is in local motion, Aquinas takes the termini of its change not to be forms of the moving body, but rather to be receptacles or containers successively filled by that body. But if that is correct, then it is hard to see how local motion could be said to involve the positing of any distinct forms to be received by or produced in matter, as P5_L and P6_L require.

But here we must take care. For even if we grant that the entities serving as the termini for local motion are not forms, it might still be thought that Aquinas takes local motion to involve the reception of distinct forms by matter. For insofar as a body comes to fill a new place (i.e., a receptacle that it did not fill previously), it will still come to be newly related to that place. And one might take the new relation itself to be a form—that is, an entity both distinct from and received by the body, as well as produced by some agent.

Now if there were such a form, it would have to be a type of accidental form, insofar as it would belong to one of the accidental categories—namely, that of spatial location or “where” (ubi). As an accidental form, moreover, it would have to be a monadic (one-place) form, since Aquinas is emphatic that no accidental form can belong to more than one subject at a time.²⁶ But, of course, if all this is right, then if there were a form involved in local motion, it would have to be a distinctive type of monadic property—one posited solely to explain how a subject of local motion is related to the places serving as its termini. The suggestion that local motion involves such a form might seem foreign to us—but it was not unheard of in the Middle Ages. John Duns Scotus, for example, seems to have held just such a view, introducing the abstract term ‘spatial locatedness’ (ubietas) precisely to refer to the special type of monadic form relating bodies to the places they fill.²⁷

But however it may be with other medieval philosophers, Aquinas himself cannot be interpreted as holding such a view. On the contrary, as I shall now show, he explicitly commits himself to denying that local motion involves positing any distinct forms in extramental reality.

2.2 Local Motion and Angelic Causation

Aquinas’s views about the relationship of local motion to extramental forms emerge most clearly in contexts where he is discussing angelic causation. For in such contexts, Aquinas is at pains to establish both (i) that local motion is the only type of bodily change that angels can directly produce, and (ii) that this is so precisely because local motion does not posit any distinct forms in matter. To see why, let us consider some of the things he says in such contexts.

Given his theological commitments, it is not perhaps surprising that Aquinas assumes that angels exist and are causally active in the physical world. But it is interesting to note that he thinks this assumption is also accepted by many philosophers who do not share his theological commitments. As he says in his treatment of angelic causation in the Summa Theologiae:

[A]ll corporeal beings are ruled (reguntur) by the angels. This is accepted not only by the holy doctors, but also by all those philosophers who have posited incorporeal substances. (ST Ia, q. 110, a. 1)

Aquinas recognizes that the existence of angels is not uncontroversial—but he thinks that those philosophers prior to him, who posit the existence of angels generally, take them to have efficient causal power or control over the physical realm. And as he tells us in his Sentences Commentary, the reason why has to do with the superiority of their nature: “Insofar as spiritual nature is superior to corporeal nature, corporeal nature must be subject to it.” (In II Sent. d. 8, q. 1, a. 2)

Although Aquinas takes for granted that angels are active in the physical world, he denies that they are capable of producing changes in bodies that involve the reception of distinct forms in matter. In fact, he makes this denial explicit in the text immediately following that just quoted:

Insofar as spiritual nature is superior to corporeal nature, corporeal nature must be subject to it—though not with respect to the reception of forms. This is because the first beginning (inchoatio) of forms in matter, which are said to be natural capacities for form in it, is from the work of the creator, whereas their actualization proceeds from the power of determinate natural agents. With respect to local motion, however, which does not require the positing of any form in what is moved, a body is subject to a spiritual power. (In II Sent. d. 8, q. 1, a. 2)

In this passage, Aquinas tells us that, although corporeal nature must be subject to spiritual nature, its subjection is not “with respect to the reception of forms” but only “with respect to local motion”—and this is precisely because local motion “does not require the positing of any form in what is moved.” Indeed, Aquinas here suggests that the natural capacity for matter to receive form, or what he calls “the first beginning of forms in matter,” must be traced to God, whereas its actualization must be traced to “natural agents”—that is, corporeal objects or bodies.

At this point we might wonder what motivates Aquinas’s denial that local motion involves positing any distinct forms in matter. Aquinas explicitly addresses this question in the Summa:

It is clear that what is produced is similar to what produces it, since every agent produces something similar to itself. And so an agent that produces natural things bears a likeness to a compound, either because (a) the agent itself is a compound, as when a fire generates a fire, or (b) because the whole compound, both its matter and form, lies within power of the agent—and this is proper to God alone.

So, then, every reception of form by matter (omnis informatio materiae) comes directly either from God or from some corporeal agent, but it does not come directly from any angel. (ST Ia, q. 110, a. 2)

Here, Aquinas begins by asserting a likeness principle that he takes to govern efficient causation—namely, that effects must be “similar to” the causes directly producing them. He then proceeds to explain how this principle excludes the possibility of an angel’s directly causing the reception of any distinct forms by matter. The effect of such a change would be a compound. But angels are simple substances, and no simple substance—or rather, no simple substance other than God, to whom all creatures bear a likeness—can be similar to a compound. For this same reason, only compounds or God can directly produce a change involving the reception of distinct forms by matter.

Although this passage continues the line of thought developed in the others we have considered, it also clarifies and extends it in certain ways. For one thing, it specifically allows there to be at least one incorporeal substance or spirit that can produce the reception of distinct forms by matter—God. For another, it explicitly restricts the ban on angelic production of these forms to direct causation. This is because Aquinas wants to leave open the possibility that angels can indirectly cause the reception of distinct forms by matter. Thus, in the same context he also says:

By first causing a local motion, angels can cause other changes through it—namely, by applying corporeal agents to the production of their own effects, just as a blacksmith uses fire to soften iron. (ST Ia, q. 110, a. 3 ad 2)

The idea here is that, even if an angel cannot directly cause some iron to receive a distinct form, such as a quality of heat or softness, it can indirectly cause that change by directly causing the iron to move closer to a fire.

As all of this helps to make clear, in his treatments of angelic causation Aquinas commits himself to each of the premises of the following argument:

Argument from Angelic Causation

Angels cannot directly produce changes in bodies that involve the reception of any distinct forms by matter.

Local motion is the only type of change that does not involve the reception of any distinct forms by matter.

Hence, local motion is the only type of change that angels can directly produce in bodies.

But, of course, if all of this is right, then Aquinas’s views about local motion cannot be governed by P5 and P6. On the contrary, far from accepting the specification of these principles introduced earlier, he instead accepts their denials—which we might represent as follows (with changes indicated in bold):

1. (P5*_L)

1. Local motion without the reception of distinct forms. For a pre-existing subject’s passive potentiality for existing in a new locative state to be actualized is not for that subject to receive a new entity—namely, a distinct form that it previously lacked.

1. (P6*_L)

1. Local motion without the production of distinct forms. A pre-existing subject’s passive potentiality for existing in a new locative state can be actualized without some efficient cause producing a new entity in it—namely, a distinct form that it previously lacked.

And, of course, it is a short step from here to the second of the two Thomistic theses giving rise to the problem of local motion:

Second Thomistic Thesis about Change

1. (T2)

1. Local motion is a type of change that cannot be analyzed in terms of the reception of any distinct forms by matter.

3.1 Solution

To prepare the way for my solution, I wish to consider one further passage from Aquinas’s discussion of angelic causation—one that offers further insight into his denial that local motion admits of hylomorphic analysis:

Now corporeal nature is lower than spiritual nature and, as is proved in Physics VIII, local motion is the most perfect of all corporeal change (motus). The reason is that something that can change its place is not, as such, in potentiality with respect to anything intrinsic, but is rather in potentiality only with respect to something extrinsic—namely, a place. And that is why a corporeal nature is capable of being moved directly by a spiritual nature with respect to place. (ST Ia, q. 110, a. 3)

Here, Aquinas is once again explaining how bodies are subject to spirits—namely, via local motion. But having insisted in the previous article that local motion does not involve the reception of any distinct forms by matter (see again the passage from ST Ia, q. 110, a. 2 cited above), he now goes a step further, suggesting that the reason why is that local motion is a type of change “with respect to something extrinsic—namely, a place.” Indeed, he suggests here that it is precisely the extrinsicness of local motion that explains why it is “the most perfect of all corporeal change.” Initially this suggestion might seem strange. But in fact there is a good reason for it. Insofar as intrinsic change involves the reception of distinct forms, it must also involve some sort of generation or corruption. But it is precisely because the heavenly bodies are incapable of undergoing any sort of generation and corruption that Aquinas takes them to be the most perfect of all corporeal substances, and hence assumes that the type of change they can undergo must be the most perfect type.

Earlier I noted that Aquinas’s four primary or per se types of change can be naturally divided into two groups—one substantial and three accidental. But as we now can see, this is not the only way they can be divided. We can also divide them into two other groups—three intrinsic and one extrinsic:

Types of Per Se Change Revisited

This further division is, in certain ways, the more important one, at least from an ontological perspective. For it is only intrinsic changes that involve reception of distinct forms by matter, and hence require the positing of some type of compound.

All of this suggests an obvious strategy for resolving the apparent tension in Aquinas’s views about change and local motion. In particular, it suggests that we take his apparently general claims about change and the reception of distinct forms to be tacitly restricted to intrinsic change. But if that is right, then we can represent Aquinas’s views about change and local motion more perspicuously as follows (once again with changes indicated in bold):

Two Thomistic Theses about Change Revisited

1. (T1*)

1. All intrinsic change can be analyzed in terms of the reception of distinct forms by matter.

1. (T2*)

1. Local motion is a type of extrinsic change that cannot be analyzed in terms of the reception of any distinct forms by matter.

The tacit restriction of Aquinas’s claims about change and hylomorphism to intrinsic change makes good sense, given how natural it is to think of change specifically in terms of intrinsic change.²⁸ In addition, this restriction seems to best fit with Aquinas’s specific association of matter, form, and privation with generation and corruption of compounds. As noted earlier, he does sometimes speak of all three as principles of change, and in this regard commentators tend to follow him. But as I also noted, more often than not, Aquinas speaks of them as principles of nature, which he specifically associates with generation and corruption.

3.2 Implications

If my solution to the problem of local motion is correct, it has a number of implications. Here I want to highlight several of the most important.