Those Two Roads: How a Natural Philosophical Solution to a Difficulty about Motion Serves Thomistic Theology

By John G. Brungardt, Ph.D.

Dedicated to the memory of Dr. Ralph M. McInerny

Introduction

GLOSSING Aristotle’s definition of motion, “the actuality of what exists in potency, as such,”[1] St. Thomas Aquinas maintains that “It is wholly impossible to define motion in another way through things prior and more known, except as the Philosopher here defines it.”[2] This is an amazing claim. Any other ways of enunciating the reality of motion—even in Aquinas’ own corpus—must be secondary and derivative descriptions, or worse.[3] Motion is, for intellects such as ours, the native intelligible light in which we understand being. Philosophical progress is measured by the degree to which we intellectually resolve changing being to its unchanging principles and causes.

            Now, there exists a fascinatingly hard knot of difficulties in regard to the definition of motion. Let us first examine the discoveries about motion that lead to the knots about motion, action, passion, and relation, and then attempt to make certain distinctions to untie them. Let us see whether and how action and passion are distinct categorical realities.[4] I indicate the importance of this difficult topic by touching on some implications it has for natural and revealed theology in conclusion.

1. Tying and Untying Some Knots about Motion

Aquinas notes of categorical relations that “Since relation has the weakest being (since it consists only in this, that it holds itself towards another), it is necessary that it be founded upon some other accident.”[5] This remark surfaces when commenting on Aristotle’s definition of motion because relations, in some sense or other, structure the reality of motion and its concomitants. For instance, the momentum of motion—the “present division” of a motion here and now—is ordered both to termini a quo and ad quem. Again, there is a relation between mover and moved. This is a conceptually immediate link, as noted in the following text:

Although it pertains to the notion of knowledge that it requires knowledge, the knower, and the thing known, nonetheless it is not required that these three differ in reality, just as in the case of the notion of motion it is the case there is the mover and the moved. But that the moved be other than the mover cannot be known except by a demonstration, before the discovery of which many were of the opinion that something could move itself.[6]

(This is to give Hume some credit.) Yet it takes a demonstration—as Aquinas notes—to realize that this relationship between mover and moved must be really distinct.

            Further insight into the relationships that give structure to motion is motivated by various “logical difficulties” in Physics III.3.[7] The solution to these difficulties results in the following overall account. First, motion is in the mobile as in a subject, because motion is the act of that subject’s potency qua mobile. Yet the act of the mover is not different from the act of the moved. Mover and moved are thereby linked: “What the mover causes by acting and what the moved receives by suffering is the same.”[8] The acts of mover and moved are not divided; otherwise, some further act would be needed to relate them as cause and effect, and a question about the identity of that act would arise. Nor is it absurd that the same act belong to two things that differ in kind, for these two kinds—the agent and patient—are related in the way that act and potency are related, and the same act of motion belongs to these different subjects in different respects:

Nothing prevents one act from belonging to two things, such that the act is not one and the same in account, while it is one in reality, as it was said above that the distance from two to one is the same as from one to two, and that which is in potency to the agent, and conversely. For thus the same act in reality belongs to two things according to a diverse account: for the act [of motion] belongs to the agent insofar as it is from it, and yet it belongs to the patient insofar as it is in it.[9]

Action is in the moved but is not “cut off” from the agent.[10] So, merely because action and passion are the same in the mobile, the agent qua agent does not suffer what it causes (that is, the teacher when teaching, and precisely qua teaching, does not learn). The teacher’s teaching activity in the student is the student’s learning, but differs “in account.” Consequently, action and passion are different, but only in account.[11] “[M]otion is called ‘action’ insofar as it is the act of the agent as from that [the mover]; however, it is called ‘passion’ insofar as it is the the act of the patient as in this [the moved].”[12]

            Nonetheless, “to teach” and “to learn” are really different:

It does not follow, even though the teaching and learning [doctio et doctrina] of the student are the same, that to teach [docere] and to learn [addiscere] are the same. Because teaching and learning are said in the abstract, while to teach and to learn are said in the concrete. Whence they are applied to the ends or the termini according to which one derives a diverse account of action and passion. For just as we may say that there is the same space between distant things, abstractly considered, nonetheless when we connect [it] to the termini of the space it is not one and the same, as when we say that this is distant from that or that from this.[13]

The key image that occurs in various forms in these texts is a road between two places, the interval between one and two, or going uphill and going downhill. On the one hand, these images usually emphasize how a sameness in the thing can still admit of a difference in the account of the thing. This seems to mean no more than a rational or mind-dependent otherness, a difference “merely in thought” or “viewpoint.”[14] Yet if the difference is only perspectival, how are action and passion different categories? On the other hand, Aquinas just used one of the variants of this image, as in the quote just above, that it is really different to go from here to there versus to go from there to here, to show that “to act” and “to suffer” are really different. 

2. Relation, Action, and Passion

So, are there two roads between Athens and Thebes? First, note that “agent” and “patient” can name distinct, causally interacting substances. Yet these substances are sometimes called by their accruing relatives, e.g., “father” and “son” or “mover” and “moved.” However, categorical relations require a foundation in a subject, and for agent–patient relationships this foundation is action and passion. Is this circular? No. In the order of being the substances as such are prior (as well as their powers to act or to be acted upon); then follows their action or passion, upon which follows the agent-patient relationship. (Why is this individual a father? Because he has generated offspring. That is, the being of the relation is explained through the prior being of the action of that substance.) Second, note that some manner of order between substances (where one stands to the other as act to potency or possible agent to possible patient) is foundational to understanding agent or patient substances with powers. To those “people [who] look for a unifying formula, and a difference, between potentiality and actuality,”[15] we say: there is none.

            Let’s return to why action and passion are different. If they are the same in substance with motion, there seems to be no escaping the axiom that things that are the same with the same are the same with each other. But “sameness” here must understood as “the same in subject and the same in account.” This is because contradictory predicates cannot be the same nor belong to the same subject in the same way. Action and passion must be distinct due to the contrariety in their accounts. What are these? Action and passion are both, as it were, “motion plus a relation.” Action is motion as from the agent in the patient; passion is motion as in the patient from the agent. This contrariety of “from” and “in” in their accounts arises due to the difference between agent and patient as substances:

Thus, it is clear that, granted that motion be one, nonetheless the predicates which are taken according to motion are two, because predicamental denominations come to be from diverse exterior things. For the agent is one thing, from which, as from something exterior, the predicament of passion is taken by way of denomination; the patient is another thing, from which the action is denominated.[16]

Thus, according to Aquinas, this extrinsic relation within action and passion rooted in really distinct termini—i.e., the patient and agent—guarantees the categorical distinction of action and passion. How is this the case? Why isn’t the relation in the accounts of action and passion merely a species in the category of relation?

            We must distinguish among real relations from rational relations and categorical relations (relativa secundum esse) from transcendental relations (relativa secundum dici). Real versus rational relations are distinguished based upon the presence or absence of certain conditions of order, namely: both relata must exist, they must be distinct in reality, and they must have some basis that makes one orderable to the other.[17] Thus, father and son are really related because both are beings, they are really distinct, and there is a basis for the order between them, namely, generation and being generated. Rational relations arise when one of the conditions is absent. In these cases, the rational relation is either attributed to relata in the mind or the relation is attributable to real things due to the mind being forced, by a kind of necessity, to relate those things precisely insofar as it understands them. This is the case because there is some remote foundation in reality even for rational relations.[18] In this latter case, we can predicate the rational relation truly of the thing: e.g., things are knowable, or tomorrow is after today.

            So, how do categorical relations differ from transcendental relations?

For things are called categorical relatives [relativa secundum esse] when names are imposed to signify the relationships themselves. However, they are called relatives secundum dici when names are imposed to signify qualities or something of the sort principally, upon which relations still follow.[19]

However, this distinction between categorical and transcendental relatives is not the same as that between real relations and rational relations:

Such a distinction between categorical relatives and transcendental relatives does not require that [the relation in question] be a real relation. For there are certain categorical relations which are not real (as right and left in a column), and there are certain transcendental relations which nonetheless import real relations (as is clear in the case of knowledge and sensation).[20]

Given the two pairs of mutually non-exclusive distinctions, we have four possibilities: relatives can be (1st) categorically real (as double and half, or father and son); (2nd) transcendentally real (as knowledge to what is known); (3rd) categorically rational (left and right in a column; or genus and species); (4th) transcendentally rational (a categorical relation to its subject).

            Now, if action or passion are “motion plus a relation,” the relations that constitute them must be transcendental relations.[21] Note that the definition of action involves the order between an agent and the motion it causes, for action is motion as from the agent into the patient. So the relata in this case are a subject (the agent) and a motion. Now, recall the ontological order we established was as follows: first a substance, then its action, then its categorical relation. Being an agent cause of motion and being a motion caused by an agent are themselves realities upon which other relations follow. Yet such is the definition of a transcendental relation. This is confirmed by the fact that this relation is between relata in different categories. The agent is a substance, and motion is an incomplete reality capable of belonging to various categories. This seems to be an implicit condition based upon the contrasting notion of a categorical relation, namely, that the foundations for the relation be of like kind or “of the same order.”[22] That is, real categorical relations cannot be founded upon something of the same order without a prior order that relates them. This order implies the possibility of a broader, transcendental type of real order, some of which ground categorical relations while others are merely transcendental relations.

            Consider the text quoted at the end of Section 1. While teaching and learning are the same, “to teach” and “to learn” are really different because the latter are said in a concrete context. That is, if we focus only on motion—in abstraction, as it were, from its concrete context—we do not include action and passion. Still, we must say that action and passion are not distinct from the actuality that is motion. However, in a more concrete consideration of the context of motion, the mind unavoidably relates motion to mover and moved, and motion as such is not a complete reality that is orderable of itself to the agent or patient via something of itself that grounds some further real relation. The motion as momentum simply is the act of the mover. Again, we say with Aristotle to those “people [who] look for a unifying formula, and a difference, between potentiality and actuality”—there is none. Thus, in the concrete, there is a real difference between to act and to suffer, and seeing motion in this light, we must assign it really diverse predicates. The road from Thebes to Athens and the road from Athens to Thebes—in the concrete order of reality as from here to there or as from there to here—are two roads. 

3. Implications

The good consists in mode, species, and order. Since the good is in things, this order must be a real order, whether categorical or transcendental, constituting the causal warp and woof of the cosmos as necessary to make the universe what it is, a certain unity of order amongst existing substances. The knots we have tried to untangle have many implications besides this. For instance, perhaps Hume is not too much to blame when failing to identify some distinct idea or percept that links cause and effect, or mover and moved. As Aquinas notes, some think that relations between things are like predicables or second intentions, merely in the mind, because of the “weakness of their being.”[23] For it is difficult to see that, first, there is a deeper or prior transcendental relation in things that links agent to patient, upon which follows a categorical relation (which is surely a “faint” perception, on his terms). Furthermore, Aristotle’s care to separate motion from the mover by placing that act of the mover in the mobile opens up the logical space necessary for the possible existence of an unmoved mover.[24] In conclusion, let us note some theological implications of the natural philosophical fact that action and passion are constituted by a transcendental relation.

            First Implication: God as Cause

Note that because motion simply is the act of the mover, the transcendental relation that constitutes the action of that mover could either imply a real relation on the side of the agent or sometimes a rational one. In univocal agents and in those agents whose perfection consists in their being actual agent causes, the agent is really related to the motion they cause in the patient. That is, such agents are transcendentally related as substances with active powers to the correlative passive potencies in other substances, and since these agent’s actuality perfects them, they have a transcendentally real relation to the action they cause. Built upon this transcendental relation follows the real, categorical relation of mover. However, this is not the case for God’s action:

God does not act through a mediating action, understood as proceeding from God and terminating in creatures. Rather, His action is His own substance, and whatsoever is in it is wholly outside the genus of created being, through which a creature is referred to God. Again, neither does something good accrue to the Creator due to the production of creatures; whence His action is utterly free, as Avicenna says. It is also clear that He is not in motion that He may act, but, absent any motion of His own, He makes changeable things. Thus it remains that in Him there is no real relation to creatures, albeit there is a relation of creatures to Him, as effects to their cause.[25]

In this way, a proper understanding of transitive agency in natural philosophy prepares one to recognize, in the via negativa, how creation is related to God and vice-versa.

            Second Implication: The Trinity

A second implication of untying the logical knots about motion, action, and passion is also noted by Aquinas. In Summa Theologiae, Ia, q. 28, a. 3, the first objection argues as follows:

Whatever things are one and the same with the same thing are the same with each other. But every relation existing in God is the same in reality with the divine essence. Therefore, the relations are not distinguished from each other in reality.[26]

Let us examine Aquinas’ reply:

According to the Philosopher in Physics III, the argument holds that whatever are one and the same with the same thing are the same with each other, in those things which are the same in reality and in account, just as a tunic and garment. However, this is not so in those which differ in account. Whence he also says there that, while action and likewise passion are the same as motion, nonetheless it does not follow that action and passion are the same, because in action there is implied a respect as that from which there is motion in the mobile, while in passion a respect as that which is from another. Likewise, while paternity is the same in reality with the divine essence, as is filiation, nonetheless these two in their proper accounts imply opposite respects.[27]

That is, what the philosopher can provide to sacred theology is a crucial exception to the axiom about sameness: a transcendental, real relation can lead to a real difference without adding something intrinsic to the being of the subject of such relations. That there are such real relations in the Godhead, however, is beyond his ken.

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[1] Aristotle, Physics, or Natural Hearing, trans. Glen Coughlin (South Bend, IN: St. Augustine’s Press, 2004), hereafter Physics, III.1, 201a10–11.

[2] St. Thomas, In Phys., lib. III, lect. 2, n. 3: “Et ideo omnino impossibile est aliter definire motum per priora et notiora, nisi sicut Philosophus hic definit.” (Leon.2.105)

[3] For instance, in his famous First Way, ST, Ia, q. 2, a. 3, c.: “Movere enim nihil aliud est quam educere aliquid de potentia in actum.” (Leon.4.31)

[4] That is, theirs are accidental modes of being not reducible to other accidents, nor are they merely a notional difference.

[5] St. Thomas, In Phys., lib. III, lect. 1, n. 6: “Cum relatio habeat debilissimum esse, quia consistit tantum in hoc quod est ad aliud se habere, oportet quod super aliquod aliud accidens fundetur.” (Leon.2.102)

[6] St. Thomas, In I Sent., d. 35, q. 1, a. 1, ad 3.

[7] These are contained in the third chapter of the Physics, Book III, which begins with implicit objections. See also Aristotle, Physics, III.3, 202a21–22. St. Thomas also points out that it is a logical or “dialectical” difficulty because there are probable reasons on both sides, see St. Thomas, In Phys., lib. III, lect. 5, n. 2 (Leon.2.112). Simplicius, On Aristotle’s “Physics 3,” (Ithaca, N.Y: Cornell University Press, 2002), 57, 58, following Eudemus, notes that the problem also arises because we could be deceived by language into assigning the reality of action to the agent as an inhering accident, in the same way that “seeing” and “hearing” are in the one who sees or hears. The evidentiary basis here—note Aristotle’s frequent appeals to teaching and learning—indicates that we are attempting to discover an insight from within our common experience of nature using certain logical tools, not via the a priori application of an extrinsic, pre-existing metaphysical apparatus (although that apparatus can be refined based upon this attempt at insight), nor based upon a specialized class of experiences undergirding mathematical physics.

[8] St. Thomas, In Phys., lib. III, lect. 4, n. 10: “[I]dem est quod movens agendo causat, et quod motum patiendo recipit.” And see Aristotle, Physics, III.3, 202a15, 202a16–18: “The actuality [of motion] is of [the moved] and from what is motive.”

[9] St. Thomas, In Phys., lib. III, lect. 5, n. 10: “[N]ihil prohibet unum actum esse duorum, ita quod non sit unus et idem secundum rationem, sed unus secundum rem, ut dictum est supra quod eadem est distantia duorum ad unum et unius ad duo, et eius quod est in potentia ad agens et e converso. Sic enim idem actus secundum rem est duorum secundum diversam rationem: agentis quidem secundum quod est ab eo, patientis autem secundum quod est in ipso.” (Leon.2.113)

[10] See Themistius, On Aristotle Physics 1–3, trans. by R. B. Todd (London: Bristol Classical Press, 2011), 88: “At the outset too it was stated that [action and passion] are one in their underlying subject but distinct in their definition. And this exposes them to no absurdity since when the activity of what produces change is one with respect to the underlying subject in both of them and comes about in what is being changed, it will not also be completely cut off, just as we also see from plain fact.”

[11] See St. Thomas, ST, Ia, q. 28, a. 3, ad 1: “[L]icet actio sit idem motui, similiter et passio, non tamen sequitur quod actio et passio sint idem, quia in actione importatur respectus ut a quo est motus in mobili, in passione vero ut qui est ab alio.” (Leon.4.324) See also, q. 45, a. 2, ad 2: “[A]ctio et passio conveniant in substantia motus, et differant solum secundum habitudines diversas, ut dicitur in III Physic.” (Leon.4.466)

[12] St. Thomas, In Phys., lib. III, lect. 5, n. 13: “Motus autem dicitur actio secundum quod est actus agentis ut ab hoc: dicitur autem passio secundum quod est actus patientis ut in hoc.” As Aristotle says: “the act of this in that and the act of that from this are different in account.” Physics, III.3, 202b21–22.

[13] St. Thomas, In Phys., lib. III, lect. 5, n. 12: “[N]on sequitur, etiam si doctio et doctrina addiscentis essent idem, quod docere et addiscere essent idem; quia doctio et doctrina dicuntur in abstracto, docere autem et discere in concreto. Unde applicantur ad fines vel ad terminos, secundum quos sumitur diversa ratio actionis et passionis. Sicut licet dicamus quod sit idem spatium distantium aliquorum, abstracte accipiendo; si tamen applicemus ad terminos spatii, sicut cum dicimus distare hinc illuc et inde huc, non est unum et idem.” (Leon.2.113)

[14] The latter two translations occur in Fr. Pierre Conway, O.P.’s, translation; see url: <https://dhspriory.org/thomas/Physics3.htm#5>; n. 320: “This motion as a matter of fact is action from one viewpoint and passion from another.” See Gloria Frost, “Aquinas’ Ontology of Transeunt Causal Activity.” Vivarium 56 (2018): 1–36, at 9 and fn. 22: “For Aquinas, distinctions according to account (secundum rationem) are not necessarily mere conceptual distinctions. Aquinas maintains that many of the accounts of things (i.e., rationes) grasped by our intellect are also found in reality. See, for instance, In I Sent., d. 2, q. 1, a. 3 (ed. Mandonnet, vol. 1, 67): ‘... ratio dicitur esse in re, inquantum significatum nominis, cui accidit esse rationem, est in re: et hoc contingit proprie quando conceptio intellectus est similitudo rei.’ Summa contra Gentiles II, c. 75 (ed. Leonine, vol. 13, 474): ‘Id vero quod intelligitur, est ipsa ratio rerum existentium extra animam ... [R]es in suis naturis existentes cognoscantur.’”

[15] Aristotle, Metaphysics, VIII.6, 1045b16. See also Metaphysics IX.1, 1046a19–29 regarding the act–potency comparison between agent and patient senses of “potency” or “power.”

[16] St. Thomas, In Phys., lib. III, lect. 5, n. 16: “Sic igitur patet quod licet motus sit unus, tamen praedicamenta quae sumuntur secundum motum, sunt duo, secundum quod a diversis rebus exterioribus fiunt praedicamentales denominationes. Nam alia res est agens, a qua sicut ab exteriori, sumitur per modum denominationis praedicamentum passionis: et alia res est patiens a qua denominatur agens.” (Leon.2.115).

[17] See St. Thomas, De Potentia, q. 7, a. 11, c.: “Ad hoc autem quod aliqua habeant ordinem, oportet quod utrumque sit ens, et utrumque distinctum (quia eiusdem ad seipsum non est ordo) et utrumque ordinabile ad aliud.”

[18] Ibid., where St. Thomas gives the following four examples of the possible cases: “Alio modo secundum quod huiusmodi relationes consequuntur modum intelligendi, videlicet quod intellectus intelligit aliquid in ordine ad aliud; licet illum ordinem intellectus non adinveniat, sed magis ex quadam necessitate consequatur modum intelligendi. Et huiusmodi relationes intellectus non attribuit ei quod est in intellectu, sed ei quod est in re.” For instance, if one or both of the relata do not exist outside the mind, as the relation between genus and species, this is attributable to mind; but neither yesterday nor tomorrow exist, and yet the mind must put one before the other. If the relata are not really distinct outside the mind, then their relation is rational, as when we relate Socrates to himself when saying that he is the same as himself. (Even though Socrates is really identical with himself, the relation between the “two” Socrates is rational; see ibid., ad. 3) The relata could lack order to each other if one of them is already a relation, as when the mind relates a relation to its subject. Finally, the relata could lack order to each other because a foundation for the relation is found only in one of them, for instance, knowledge is really related to the known, but not vice versa. Also, bilateral symmetry (having left and right) in a non-biological thing like a rock or column is such a case as this; see ibid., and also St. Thomas, In Phys., lib. V, lect. 3, n. 8 (Leon.2.237).

[19] St. Thomas, De Potentia, q. 7, a. 10, ad 11: “Dicuntur enim relativa secundum esse, quando nomina sunt imposita ad significandas ipsas relationes; relativa vero secundum dici, quando nomina sunt imposita ad significandas qualitates vel aliquid huiusmodi principaliter, ad quae tamen consequuntur relationes.”

[20] Ibid.: “[D]istinctio ista relativorum secundum esse et secundum dici, nihil facit ad hoc quod sit relatio realis. Quaedam enim sunt relativa secundum esse quae non sunt realia, sicut dextrum et sinistrum in columna; et quaedam sunt relativa secundum dici, quae tamen important relationes reales, sicut patet de scientia et sensu.”

[21] Compare John of St. Thomas, Cursus Philosophicus, II, q. 14, a. 2; also, q. 19, a. 1, I:624b33–625a4: “[I]sta praedicamenta dependere ab aliquo extrinseco existente, non ut a termino, sicut relatio secundum esse, sed ut a principio et forma a qua originatur, vel cira quam versatur denominatio; et iste respectus est secundum dici, vel transcendentalis, quia licet dependeat ab existentia illius extrinseci, ut actu existenter denominet, tamen quia essentialiter et per se a tali extrinseco dependet, sicut ubi a loco, actio ab effectu, etc., ideo dicitur illa relatio transcendentalis et secundum dici. Relatio autem secundum esse non consistit in hoc solum quod pendeat ab existentia termini ut actu existat, quod aliis est commune, sed quod sit ad illum solum ut ad purum terminum.”

[22] See St. Thomas, De Pontentia, q. 7, a. 10, c.: “Ad cuius evidentiam sciendum est, quod cum relatio realis consistat in ordine unius rei ad rem aliam, ut dictum est; in illis tantum mutua realis relatio invenitur in quibus ex utraque parte est eadem ratio ordinis unius ad alterum: quod quidem invenitur in omnibus relationibus consequentibus quantitatem.” Here, the problem is that an order can be found between so many things in many categories, and thus relations would multiply beyond what seems true. Recall that Aristotle’s treatment of relation in the Categories begins without distinguishing between relations secundum esse and secundum dici, and then Aristotle redefines relation to include only relations secundum esse. The first attempt at defining relation (6a36–37) yields “We call relatives all such things as are said to be just what they are, of or than other things, or in some way in relation to something else,” while the second, more precise attempt (8a31–32) gives us “those things are relatives for which being is the same as being somehow related to something.” This latter definition is arrived at to avoid a multiplication of relations that would include even substances as relations, at 8a29–30: “Now if the definition given above was adequate, it is either exceedingly difficult or impossible to reach the solution that no substance is spoken of as a relative.”

[23] St. Thomas, De Potentia, q. 7, a. 10, c.: “Dicendum quod relatio ad Deum est aliqua res in creatura. Ad cuius evidentiam sciendum est, quod sicut dicit Commentator in XI Metaph., quia relatio est debilioris esse inter omnia praedicamenta, ideo putaverunt quidam eam esse ex secundis intellectibus. Prima enim intellecta sunt res extra animam, in quae primo intellectus intelligenda fertur. Secunda autem intellecta dicuntur intentiones consequentes modum intelligendi: hoc enim secundo intellectus intelligit in quantum reflectitur supra se ipsum, intelligens se intelligere et modum quo intelligit. Secundum ergo hanc positionem sequeretur quod relatio non sit in rebus extra animam, sed in solo intellectu, sicut intentio generis et speciei, et secundarum substantiarum.”

[24] Regarding this, see R. Glen Coughlin’s “Translator’s Endnotes” in Physics, 62, n. 15: “Aristotle has argued that the act of the mover is in the mobile. The hot iron heats the water, and though the iron is cooled in return, this is accidental to it as a mover. Moreover, since the action of heating is in the water, not in the iron, the act of the mover as a mover is not in itself, but in the patient, the thing which undergoes the motion. All of this leaves open the possibility that there be an unmoved mover, though it does not establish that there is one or even that one is finally possible. For there may be other objects which we have not thought of. We will not finally establish this possibility, or that of an immaterial being, until we show that there really is such a thing.”

[25] St. Thomas, De Potentia, q. 7, a. 10, c.: “Deus autem non agit per actionem mediam, quae intelligatur a Deo procedens, et in creaturam terminata: sed sua actio est sua substantia, et quidquid in ea est, est omnino extra genus esse creati, per quod creatura refertur ad Deum. Nec iterum aliquod bonum accrescit creatori ex creaturae productione, unde sua actio est maxime liberalis, ut Avicenna dicit. Patet etiam quod non movetur ad hoc quod agat, sed absque omni sua mutatione mutabilia facit. Unde relinquitur quod in eo non est aliqua relatio realis ad creaturam, licet sit relatio creaturae ad ipsum, sicut effectus ad causam.”

[26] St. Thomas, ST, Ia, q. 28, a. 1, obj. 1: “Quaecumque enim uni et eidem sunt eadem, sibi invicem sunt eadem. Sed omnis relatio in Deo existens est idem secundum rem cum divina essentia. Ergo relationes secundum rem ab invicem non distinguuntur.” (Leon.4.324)

[27] Ibid., ad 1: “Secundum philosophum in III Physic., argumentum illud tenet, quod quaecumque uni et eidem sunt eadem, sibi invicem sunt eadem, in his quae sunt idem re et ratione, sicut tunica et indumentum, non autem in his quae differunt ratione. Unde ibidem dicit quod, licet actio sit idem motui, similiter et passio, non tamen sequitur quod actio et passio sint idem, quia in actione importatur respectus ut a quo est motus in mobili, in passione vero ut qui est ab alio. Et similiter, licet paternitas sit idem secundum rem cum essentia divina, et similiter filiatio, tamen haec duo in suis propriis rationibus important oppositos respectus. Unde distinguuntur ab invicem.” For a helpful overview, see Gilles Emery, “Ad Aliquid: Relation in the Thought of St. Thomas Aquinas,” in Theology Needs Philosophy: Acting against Reason Is Contrary to the Nature of God, ed. Matthew L. Lamb (Washington, DC: Catholic University of America Press, 2016), 227–39, and Emery’s “Central Aristotelian Themes in Aquinas’s Trinitarian Theology,” in G. Emery and M. Levering, eds., Aristotle in Aquinas’s Theology (Oxford: Oxford University Press, 2015), 1–28.