At the end of his commentary on Aristotle's Physics, St. Thomas Aquinas says that Aristotle has ended his discussion on nature by considering the First Principle of all nature, which is God, above all and blessed forever: Et sic terminat philosophus considerationem communem de rebus naturalibus, in primo principio totius naturae, qui est super omnia Deus benedictus in saecula. Amen. However, this has raised much confusion and debate.
Two Problems
In this article, I want to address two problems with this surprising claim at the end of St. Thomas's Commentary on the Physics.
First, it might seem that Aristotle, who in the Physics is dealing with physical motion, does not demand in the Physics a completely separate substance, but only requires an ensouled heavenly body, whose soul would be a physically unmoved mover. Indeed, St. Thomas's exposition of Aristotle's second argument from motion in the Summa Contra Gentiles may appear to show that St. Thomas is aware of this. There seems to be the claim in this argument that we must appeal to the Metaphysics in order to show that there is a separate Unmoved Mover, higher than any physically unmoved part of a self-mover.
Second, even if we grant that St. Thomas regards Aristotle's Physics as ending with a completely separate substance, why must that separate substance be God? St Thomas recognises that there are many separate substances in reality (angels) and that God, the ipsum esse subsistens, is radically different from all of them.
Summary of Solution to the First Problem
The explicit claim from the end of the Commentary on the Physics quoted above simply does not sit well with Jean Paulus's subordinationist thesis.1 This claims that St. Thomas did not think that Aristotle's Physics concludes with the Unmoved Mover of the Metaphysics. Instead, it concludes with a soul of a celestial body, the final cause of whose motion is an Unmoved Mover discovered exclusively in the Metaphysics.
On the other hand, Anton Pegis also seems to be mistaken when he claims that St. Thomas sees only the Physics as demonstrating that Unmoved Mover described in the Metaphysics.2 According to him, the Metaphysics just describes its relation to the celestial self-movers beneath. Pegis has to very awkwardly re-interpret a statement in the second argument from motion in the Summa Contra Gentiles, which seems rather explicitly to have Aristotle, in the Metaphysics, arguing from a first self-moving ensouled celestial body to a completely separate substance.
In fact, St. Thomas did think that Aristotle's Physics terminates in a completely separate immaterial substance. The first argument from motion in the Summa Contra Gentiles is mostly derived from Physics VII, but it can be seen to be a basic sketch of what we can refer to as 'the proof from the Physics' and as implicitly requiring the further elucidation and development of Physics VIII. However, there is a distinct proof from the Metaphysics, and this the essence of the second argument from motion in the Summa Contra Gentiles, even though that argument instrumentally utilises already established background claims from Physics VIII. This 'proof from the Metaphysics' is simply another way to establish the existence of a completely separate immaterial substance.
Summary of Solution to the Second Problem
To the second problem, I shall argue that, if 'God' is understood with a nominal definition of something like 'highest and first principle of the universe', then St. Thomas sees that Aristotle identifies the Unmoved Mover of the first heavenly sphere as being this first and highest principle. And from the fact that the Prime Mover is the highest and first principle of the universe, St. Thomas thinks that Aristotle can and does draw out properly divine attributes to describe it. As it turns out, and as can be seen from his de Substantiis Separatis, St Thomas thinks that Aristotle is wrong to identify the immediate mover of the first heavenly sphere with the highest and first principle of the universe. Instead, St. Thomas posits a whole range of choirs of angels in between the angelic unmoved mover of the first heaven and the highest separate substance (God). However, according to St. Thomas, the fact that the highest separate substance is radically different from the other separate substances in being Pure Act, Provident Ruler of the Universe, and the Maximal Being who is the cause of all other being, can be metaphysically established from his status as the highest existing separate substance. And so, whether we say that the highest existing separate substance will be the mover of the first heavenly sphere or will be a higher being than the mover of the first heavenly sphere, we can still determine that the highest separate substance is God. Given that Aristotle identifies the highest separate substance (God) with the mover of the first heavenly sphere, St Thomas can accurately say that Aristotle has ended with God - the same God, who must be Ipsum Esse Subsistens and a Creator ex nihilo. Furthermore, Aristotle's reasoning from motion is not useless according to St. Thomas, since it shows us the need for a separate substance who, disjunctively, must either be God or must be subordinated to further separate substances, the highest of which will be God.
Physical Motion and how it requires an Unmoved Mover
In the Physics, Aristotle has been talking exclusively about motion (κίνησις) in the strict sense, which encompasses change in 1) place, 2) quality, or 3) quantity, the subject of which can only be a material, sensible, divisible body. Such a change is a continuous, gradual, imperfect act, measured by time, which terminates in the perfect act that is the end of motion. These are opposed to instantaneous acts, such as seeing or knowing.
Some of these continuous motions are the result of an exterior agent drawing out an inert potency in a patient. For example, a stone may be at rest where it happens to be located. It is, by nature, indifferent to being located at a different horizontal location. But then, someone kicks it and it is moved horizontally to another place. However, some motions are natural and not violent. For example, when I simply let go of a stone in my hand. Aristotle and St. Thomas would call me a per accidens cause of the stone's motion, insofar as I remove an impediment to its natural motion, but the the actual motion of the stone just follows from its nature. A stone will fall down to rest in its 'natural place.' The only per se mover of the stone is the generator of its nature. But once the generator has granted it its nature and form, the motion follows spontaneously. In such cases, St. Thomas emphasises that these natural motions are ordered to rest in a natural place. There can be no motion for the sake of motion. The natural body only naturally moves precisely because it is ordered to resting in its natural place. Take away the latter, and you remove the ratio for natural motion.
But manifestly, the elements of this variable sublunary world do not exist in a state of permanent rest in their natural places. This is because this is a world of generation and corruption. The cycles of the heavenly bodies, according to Aristotle and St. Thomas, cause substantial changes in the sublunary elements, which explains why there are elemental cycles of generation and corruption. The Sun is nearer and generates air from water, which rises up. It is further away, and the air is substantially changed back into water, which falls down. For Aristotle and St. Thomas, these elemental cycles are dependent on the continuous circular motions of the heavenly bodies.
But St. Thomas emphasises that the continuous circular motions of the heavenly bodies cannot be the result of a spontaneous natural motion, precisely because they are continuous circular motions. These motions are not ordered to rest in a natural place. Therefore, the question can be raised why they happen.
If they are not the result of natural motion, neither can they be the result of self-motion, if by that is meant what Aristotle and St Thomas call primo et per se self-motion. If we are to speak of self-motion, then we must speak of one part moving another part.
But then, anything which must itself be moved in order to cause motion, must ultimately be reduced to a mover which does not need to be moved in order to cause motion. This is what we can call an 'unmoved mover.' The motion of the heavenly bodies require such an unmoved mover to explain their motion. By consequence, such an unmoved mover would be responsible for the generation, corruption, and motion caused in the sublunary realm by means of the heavenly body which it moves.
How can an Unmoved Mover thus derived be identified with God?
Such an unmoved mover causes motion in the strict sense (namely local motion) in the celestial bodies without itself being subject to motion in the strict sense. However, if our scope is limited to motion in it's strict sense, then the 'unmoved' in such an unmoved mover must be limited to meaning 'not subject to motion in its strict sense' (ie. change in place, quality, quantity). If this is all Aristotle's Physics concludes to, how can such a being be straightaway identified with God? Following the principles of Aristotle and St. Thomas, we can conclude, for various reasons that such a being must be immaterial and intelligent. However, such a being could be a soul or a separate substance other than God.
Moreover, in Metaphysics Λ (known to St. Thomas as Metaphysics Book XII), Aristotle distinguishes between:
1) a class of self-movers, who are ensouled heavenly spheres, and whose physically unmoved immaterial souls are the efficient causes of the motion of their material bodies, and
2) a class of separate unmoved movers who 'move' the appetite of those self-movers as final causes, (where 'move' is an analogous and metaphorical use of the word, rather than motion in the strict sense). Amongst these is the Unmoved Mover of the first heaven (the outermost heaven, which is the sphere of the fixed stars), which we can refer to as the Prime Mover.
Confusion and Clarification from The Two Ways from Motion in the Summa Contra Gentiles
In Summa Contra Gentiles cap. 13, St. Thomas gives 5 proofs by which Philosophers and Catholic Doctors have proved there to be a God (procedamus ad ponendum rationes quibus tam philosophi quam doctores Catholici Deum esse probaverunt). The first two are taken from Aristotle, who intended, in two ways, to prove that there is a God from a consideration of motion (Primo autem ponemus rationes quibus Aristoteles procedit ad probandum Deum esse. Qui hoc probare intendit ex parte motus duabus viis). The two ways from motion which St. Thomas proceeds to place before us each end with the conclusion of a first immobile mover (primum movens immobile).
However, surprisingly enough they operate with different extensions of the term 'motion.' The first argument from motion limits its scope to a consideration of physical motion, which I have described above as 'motion in the strict sense.' Whereas the second argument extends 'motion' also to a metaphorical or analogical use of the term, namely the appetite of an immaterial soul being 'moved' by a final cause.
This distinction between the two different extensions of 'motion' is verified by a note at the end of the demonstration of the first premise in the first argument. Here, St. Thomas says that it ought to be known that Plato considers every mover to be moved because he has a more general use of the term (communius accepit nomen motus), which extends also to any operation (pro qualibet operatione), such as understanding or opining; whereas, Aristotle uses the term properly (proprie) to refer to physical motion in the strict sense (actus existentis in potentia secundum quod huiusmodi), which only applies to divisible and corporeal things (qualiter non est nisi divisibilium et corporum), as is proved in Physics VI. St. Thomas briefly notes that Aristotle also touches upon Plato's use of the term in De Anima III (in which he describes the appetite as 'in a way' moved by the appetible object). But then, St. Thomas says that it doesn't matter (nihil enim differt) whether we come to a first self-mover under Plato's definition of motion (devenire ad aliquod primum quod moveat se secundum Platonem), who 'moves' inasmuch as it understands itself, and wills or loves itself (dicebat primum movens seipsum movere quod intelligit se et vult vel amat se), or whether we come to an altogether immobile mover according to Aristotle's proper definition of motion (devenire ad primum quod omnino sit immobile secundum Aristotelem).
This first argument from motion has mostly drawn from the argument at the beginning of Physics VII which argues that 1) everything which is physically moved is moved by another and 2) there cannot be an infinite chain of such moved movers. That argument at the very least concludes to a mover who causes physical motion without being physically moved. Yet, how can St. Thomas then say: 'and this we call God' (et hoc dicimus Deum)?
In the second argument, St. Thomas considers that such a physically unmoved mover must either be a completely immaterial separate substance or an unmoved part of a self-mover, namely a soul. Note that at this point, St. Thomas is, for now, restricting motion to the strict sense as used in the first argument, even though he will subsequently broaden the meaning of 'motion' to include an appetite being moved by a final cause. So, as far as physical motion is concerned, St Thomas says that we must come either to a completely separate immaterial substance or to an immaterial soul that moves its celestial body.
If we attach to the term 'God' a broad nominal definition like 'the highest first principle of the universe,' it seems right now that we can only say that 'God' is either a separate substance or an immaterial part of self-mover. But, St. Thomas knows that the latter is not the case. It is then that St Thomas expands the meaning of motion to include an appetite being moved by a final cause, to prove the truth 'that God is not part of a self-mover' (Sed quia Deus non est pars alicuius moventis seipsum...). Note that the phrase 'that God is not a part of a self-mover' presupposes a common term that understands 'God' up until now as something that can be identified either with part of a self-mover or a completely separate substance, but shall now be demonstrated as being inapplicable to a part of a self-mover. For this, St. Thomas uses Aristotle's discussion of an altogether separate mover who is higher than the soul of a heavenly body. This shows that the highest principle of the universe cannot be the soul of the heavenly body, and therefore that God is not a soul of a heavenly body.
St. Thomas says: 'But because God is not part of any self-mover, Aristotle, in his Metaphysics, further investigates, from this mover which is part of a self-mover, another altogether separate mover, which is God. For, since every self-mover moves through appetite, it must be that the mover which is part of the self-mover moves on account of appetite for some appetible. This is superior to it in moving: for the one appetising is in a way a moved mover, whereas the appetible is altogether an unmoved mover. There must therefore be a separate altogether immovable first mover, who is God.' In Latin: Sed quia Deus non est pars alicuius moventis seipsum, ulterius Aristoteles, in sua metaphysica, investigat ex hoc motore qui est pars moventis seipsum, alium motorem separatum omnino, qui est Deus. Cum enim omne movens seipsum moveatur per appetitum, oportet quod motor qui est pars moventis seipsum, moveat propter appetitum alicuius appetibilis. Quod est eo superius in movendo: nam appetens est quodammodo movens motum; appetibile autem est movens omnino non motum. Oportet igitur esse primum motorem separatum omnino immobilem, qui Deus est.
Clearly, contra Anton Pegis, St. Thomas is saying that Aristotle argues in the Metaphysics from a non-physically moved part of a self-mover to an altogether separate first mover who 'moves' the appetite of the self-mover as a final cause.
Th existence of a completely Separate Substance also apparently reached in the Physics
However, contra Jean Paulus, the fact that there must be an unmoved mover that is a wholly separate substance is not, for Aquinas, only able to be demonstrated from the Metaphysics. Rather, in his Commentary on the Physics, it is clear that St. Thomas thinks that such a wholly separate substance can also be demonstrated from the Physics. In Lectio 23, it appears that, whether rightly or wrongly, St. Thomas takes Aristotle to be talking about the kind of Unmoved Mover in the Metaphysics: an altogether separate substance. He takes Aristotle's argument that the Unmoved Mover of the Physics has no magnitude (ie. is immaterial) to mean not only that this Unmoved Mover is not a body, but that is not even a power (virtus) within a body. Aristotle 'says that, from what was previously determined, it is manifest that it is impossible that the first immobile mover has any magnitude' (Et dicit quod ex praedeterminatis manifestum est, quod impossibile est primum movens immobile habere aliquam magnitudinem). But St. Thomas goes on: 'either that it itself is a body, or that it is a power in a body' (vel ita quod ipsum sit corpus, vel quod sit virtus in corpore). Then, after emphatically describing its immateriality, complete lack of magnitude, indivisibility, that it has no part, has limitless power, that it exists outside the genus of magnitude (et etiam sicut omnino nullam habens magnitudinem, quasi extra genus magnitudinis existens) etc., St. Thomas concludes: Et sic terminat philosophus considerationem communem de rebus naturalibus, in primo principio totius naturae, qui est super omnia Deus benedictus in saecula. Amen.
For Aquinas's Aristotle at the end of Physics VIII (which the second argument from the Summa Contra Gentiles does not deal with, but instead goes the route of the Metaphysics argument), the Unmoved Mover there described can neither be a body nor a virtus in a body. Whether or not this follows from Aristotle's demonstration of the Unmoved Mover of the Physics lacking magnitude, this is what St. Thomas thought it led to. The Unmoved Mover of the Physics must, for St. Thomas, necessarily be a completely separate substance, like the separate substances of the Metaphysics. Now, although there are several separate substances discussed in the Metaphysics, there is also a Prime Mover who moves the first heaven, and upon this Prime Mover, according to Aristotle's own words in Metaphysics Λ, depends all the heavens and the earth.
One could make the following objection against Aquinas's interpretation. Aristotle deduces the lack of magnitude of the Unmoved Mover of the Physics from the fact that it must have infinite power, which is in turn deduced from the fact that it moves in an infinite time. However, the celestial self-movers in the Metaphysics move in an infinite time, and therefore must have infinite power, and therefore have no magnitude, which for Aquinas must mean that they are are completely separate substances. But this is false, since the celestial self-movers of the Metaphysics are ensouled and animated heavenly spheres, not completely separate substances. However, St. Thomas does have an answer to this. In his Commentary on the Metaphysics (Book XII, Lectio VIII, 2550), St. Thomas says that the soul of a celestial self-mover cannot have infinite power, but can only move for an infinite time as a result of the influentia it receives from the Prime Mover, which does indeed have infinite power (Non autem potest dici virtus caelestis corporis infinita, etiam si infinito tempore moveat inferiora corpora; quia non movet nisi motum. Et ita influentia est ex primo movente). Again, he positively says that there cannot be an infinite power in a celestial body, even if it moves for an infinite time, since there is not in it the active power of its being, but only a received power; its infinite duration shows the infinite power of an exterior principle, from which it receives incorruptible being, even though, on the supposition that it does so, it is truly incorruptible (Sed nec etiam potest dici quod in corpore caelesti sit virtus infinita, etsi infinito tempore esse habeat; quia in eo non est virtus activa sui esse, sed solum susceptiva. Unde infinita eius duratio ostendit virtutem infinitam exterioris principii. Sed ad hoc quod ipsum suscipiat incorruptibile esse ab infinita virtute, requiritur quod in ipso non sit principium corruptionis, neque potentia ad non esse). And yet, the Physics shows the need for eternal physical motion to be accounted for by an infinite power. For St. Thomas, this can only reside in a completely separate and immaterial substance. Therefore, the Physics shows the need for a completely separate and immaterial substance.
How to look at the two arguments from motion in the Summa Contra Gentiles
Therefore, the first argument from motion of the Summa Contra Gentiles must not necessarily rely upon the argumentation of the Metaphysics (as the second argument does), but rather we could see this first argument as an incompletely developed summary argument, as in Physics Book VII, into which we should implicitly read the further demonstrations and clarifications found in Physics Book VIII, and those claims found at least in St Thomas's interpretation of Physics Book VIII.
Therefore, the two arguments from motion in the Summa Contra Gentiles should not be seen as 1) 'argument from Physics VII' and then 2) 'argument from Physics VIII plus a corrective Metaphysics XII', but rather 1) ' summary argument from Physics VII, which implicitly requires clarification from the more detailed analysis and argumentation of Physics VIII' and then 2) 'argument from the Metaphysics explicitly utilising elements from Physics VIII.'
For Aquinas and Aquinas's Aristotle, the consideration of physical motion in the Universe means that there is required a Separate Substance as an ultimate source of motion, even if there are intermediary celestial self-movers like those discussed in Metaphysics. Whereas in the Metaphysics, Aristotle goes another route, and reasons from such celestial self-movers to Separate Substances, which 'move' celestial souls' appetites as final causes. Interestingly, according to Aquinas, this means that they moved by the higher movers inasmuch as they desire to be 'assimilated' to those higher movers in causing (in causando). In other words, they wish to imitate the higher movers in the very matter of causing. Again, whether this actually is Aristotle's view is besides the point for the purposes of this article.
Whether or not he is right, Aquinas thinks that Aristotle in the Physics (namely Physics VIII, and incompletely but implicitly in Physics VII) demonstrates the Unmoved Mover type of the Metaphysics. The argumentation in Physics VII and the the first argument from motion in the Summa Contra Gentiles are prima facie insufficient to accomplish this fully, but actually require the fuller argumentation and clarification of Physics VIII. We may say that it is unfortunate that St. Thomas did not explicitly supplement his first argument in the Summa Contra Gentiles with what he takes to be Physics VIII's demonstration that there is an Unmoved Mover which is a completely separate substance. Regardless, it remains the case that Aquinas thinks that are such grounds within Physics VIII, and not just in Metaphysics Λ.
But is a 'Separate Substance' enough?
There is another problem. St Thomas thinks that Aristotle concludes to a separate substance in Physics VIII; but why is this God? The many angels that exist in reality are separate substances, and Aristotle himself admits of a plurality of separate substances or unmoved movers.
Why St. Thomas recognises Aristotle's Prime Mover as God
The reason lies in the fact that Aristotle identifies the Prime Mover, the Unmoved Mover of the first heavenly sphere, which Aristotle indeed calls God (θεὸς), as the highest principle in the Universe: 'upon such a principle does heaven and nature depend' (ἐκ τοιαύτης ἄρα ἀρχῆς ἤρτηται ὁ οὐρανὸς καὶ ἡ φύσις, Met. Λ.7, 1074b14).
Commenting upon this, St. Thomas shows that he understands Aristotle's Prime Mover not just to move the first heaven as a final cause, but also to be responsible for its very substance: Ex hoc igitur principio, quod est primum movens sicut finis, dependet caelum, et quantum ad perpetuitatem substantiae suae, et quantum ad perpetuitatem sui motus; et per consequens dependet a tali principio tota natura, eo quod omnia naturalia dependent a caelo, et a tali motu eius (Book XII, Lectio VII, 2534: 'therefore, upon this principle, which is the first mover as an end, depends the heaven, both as to the perpetuity of its substance and as to the perpetuity of its motion, and, consequently, the whole of nature depends on such a principle, inasmuch as all natural things depends upon the heaven and on such a motion as is theirs').
Now, whether or not this is true of Aristotle himself, Aquinas thought that Aristotle regarded the Prime Mover not just as a Final Cause of motion but also as an efficient Creator of the Universe, who was a Causa Essendi as well as a Causa Movendi. This is partly because of Aquinas's interpretation of Aristotle's dictum in Metaphysics II (also known as Book α or 'Little Alpha') that just as fire is the most hot thing and the cause of heat in other things, so what is highest in being and truth is the cause of being and truth in other things (cf. Met.α.1).
In the Metaphysics, Aristotle talks about the perfection, intellection, and life of the Prime Mover. St. Thomas's comments (Book XII, Lectio VIII) on this section (Met. Λ.7, 1072b15-1073a13) are very elucidating as to how he interprets Aristotle's Prime Mover.
For St. Thomas, Aristotle has shown that there is a certain intelligible substance which is per se subsistens, with which we are now dealing with (2542: Est tamen aliqua substantia intelligibilis per se subsistens, de qua nunc agit).
This First Mover which is an intelligent and intelligible substance is to the intellect of the first moved mover (the first ensouled heaven which it moves as an intelligible and appetitible) as the Platonists thought the separate intelligible forms were to our intellect (as opposed to the Aristotelian notion of the human intellect's abstraction of intelligible forms from sensible things), through which 'contact and participation,' the first moved mover's intellect is made to be in act (ibid: Oportet enim esse primum movens substantiam intelligentem et intelligibilem. Relinquitur igitur, quod talis est comparatio intellectus primi mobilis ad illam primam intelligibilem substantiam moventem, qualis est secundum Platonicos comparatio intellectus nostri ad species intelligibiles separatas, secundum quarum contactum et participationem fit intellectus actu, ut ipse dicit). Therefore, the intellect of the first moved mover becomes understanding in act through some sort of contact with the first intelligible substance (Unde intellectus primi mobilis fit intelligens in actu per contactum aliqualem primae substantiae intelligibilis).
St. Thomas goes on to say that that on account of which something is 'such' is that 'such' in a greater degree (2543: Propter quod autem unumquodque tale, et illud magis). To understand and to delight are 'divine and noble' activities, and if they are found in the moved intellect described above which is making contact, then they are much more to be found in the first intelligible with which it makes contact, and therefore the consideration of such a thing is most delectable and the best, and a first intelligible of such a kind is called 'God' (ibid: Et ideo sequitur quod quicquid divinum et nobile, sicut est intelligere et delectari, invenitur in intellectu attingente, multo magis invenitur in intelligibili primo quod attingitur. Et ideo consideratio eiusdem, et delectabilissima est et optima. Huiusmodi autem primum intelligibile dicitur Deus).
This God is Life itself (2544: Et dicit quod Deus est ipsa vita), for the act of the intellect is a kind of life and the most perfect kind of life (ibid: actus intellectus, idest intelligere, vita quaedam est, et est perfectissimum quod est in vita). Now, whereas the first moved mover has such a life of intellection by participation and by contact with the First Intelligible, and so has an intellect which stands in potency to that act, that First Intelligible and First Intellect has this life essentially, more perfectly, in the highest degree, and does not stand in potency to this act, but is this very act essentially. This means that its intellect is identical with its very act of understanding, for otherwise it would be compared to that act as potency to act, which is contrary to what was earlier said about its substance being act (ibid: Sed illud primum, scilicet Deus, est ipse actus. Intellectus enim eius est ipsum suum intelligere. Alioquin compararetur ad ipsum ut potentia ad actum. Ostensum autem est supra, quod eius substantia est actus.)
According to St. Thomas, therefore, the Prime Mover of Aristotle has what can only be described as Divine Attributes. St. Thomas understands Aristotle as meaning his Prime Mover to be the highest principle of the whole universe, upon which all the universe depends, and to be Unreceived and Pure Act, a Supreme Intelligence whose intellect and act of intelligence are one and the same, involving no composition of act and potency, not participating in another, but a substantia intelligens et intelligibilis per se subsistens. In other words, St. Thomas sees that the God he worships is identified by Aristotle with the Unmoved Mover of the first heavenly sphere.
Even though Aristotle identified a first and highest Separate Substance which can only be called God, it was not necessary that he identified it as the immediate mover of the first heavenly sphere
Now, St. Thomas is not in fact beholden to agree with Aristotle that God is the first immediate Unmoved Mover of the first heavenly sphere. In fact, St. Thomas disagrees considerably with Aristotle description of the cosmos. For St. Thomas, there are no animated heavens, no self-moving ensouled celestial bodies, just as there is no eternal motion and eternal world. Instead, he attributes the motion of the heavenly spheres exclusively to separate substances, which St. Thomas understands to be 'angels.' And, in fact, even the first heavenly sphere, is, according to St. Thomas moved directly by an angel, both as efficient cause and as the proximate end.
That being said, Aristotle, according to St. Thomas, did identify a first and highest separate substance, with divine attributes, and which is indeed God. It just was not necessary that he identified it with the immediate mover of the first heavenly sphere. This does not mean that, for St. Thomas, all of Aristotle's reasoning in the Physics and Metaphysics is useless. Having arrived at a separate substance which causes the motion of the first heaven, then we can make a disjunction:
a) we can either stop and identify this as the highest separate substance and ultimate principle of the whole universe, who is pure act and per se existent, upon which everything else depends both for its substance and its motion, or
b) we can say that there may be a yet higher separate substance. But, nevertheless, whether there is one higher separate substance or many, the highest of these must necessarily be the ultimate principle of the whole universe, who is pure act and per se existent, upon which everything else depends, ie. God
The highest separate substance, whether the immediate mover of the first heaven (as Aristotle thought it was), or one that is higher still, must be God.
To main this interpretational balance, an illuminating text is St. Thomas's treatise, de Substantiis Separatis. In de Substantiis Separatis cap. 2, St. Thomas explicitly rejects much of Aristotle's assumptions. According to Aristotle, between us and the highest God, there is only a twofold order of intellectual substances, namely separate substances, which are the ends of the celestial motions, and the souls of the orbs which are movers through appetite and desire (Sic igitur secundum Aristotelis positionem inter nos et summum deum non ponitur nisi duplex ordo intellectualium substantiarum, scilicet substantiae separatae quae sunt fines caelestium motuum, et animae orbium quae sunt moventes per appetitum et desiderium).
For one thing, Aristotle's belief that we can determine the number of separate unmoved movers from the number of heavenly bodies is challenged: inconveniens videtur immateriales substantias ad numerum corporalium substantiarum coarctari. Unlike Plato, Aristotle did not consider the existence of separate substances below the movers of the heavens, and, more significantly for this article, he did not consider separate substances above them.
For, among beings, the superior ones are not for the sake of the inferior ones, but rather the other way round, since that which something is for the sake of is nobler than it (Non enim ea quae sunt superiora in entibus sunt propter ea quae in eis sunt inferiora, sed potius e converso, id enim propter quod aliquid est nobilius est). Therefore, we cannot determine the number of intellectual substances from the number of corporeal substances, just as we cannot determine the magnitude and number of the celestial bodies from the earthly bodies:
rationem autem finis non sufficienter aliquis accipere potest ex his quae sunt ad finem, sed potius e converso: unde magnitudinem et virtutem superiorum rerum non sufficienter aliquis accipere potest ex inferiorum rerum consideratione. Quod manifeste apparet in corporalium ordine: non enim posset caelestium corporum magnitudo et numerus accipi ex elementarium corporum dispositione, quae quasi nihil sunt in comparatione ad illa. Plus autem excedunt immateriales substantiae substantias corporales quam corpora caelestia excedant elementaria corpora; unde numerus et virtus et dispositio immaterialium substantiarum ex numero caelestium motuum sufficienter apprehendi non potest.
Then St. Thomas uses Aristotle's own argumentation to critique him. Aristotle assumes that there cannot be any motion in the heaven unless it is ordered towards the delatio of something (to be honest, I'm not quite sure what this precisely means here). This is probable enough because all the substances of the celestial orbs seem to be for the sake of the stars, which are nobler among the celestial bodies and have a more manifest effect (Assumit enim quod nullus motus potest esse in caelo nisi ordinatus ad alicuius delationem: quod satis probabilitatem habet, omnes enim substantiae orbium esse videntur propter astra, quae sunt nobiliora inter caelestia corpora et manifestiorem effectum habentia). Further, he assumes that all the superior impassible and immaterial substances are ends, since they are inherently the best (Ulterius autem assumit quod omnes substantiae superiores impassibiles et immateriales sunt fines, cum sint secundum se optima). This makes sense because the good has the ratio of end, so that those things which are inherently the best among beings are the ends of the others (et hoc quidem rationabiliter dicitur, nam bonum habet rationem finis, unde illa quae sunt per se optima in entibus sunt fines aliorum). But the fact that they are ends of lesser beings because they are better does not necessitate the conclusion that their number is to be equated with the number of those lesser beings (Sed quod concludit hunc esse numerum immaterialium substantiarum qui est caelestium motuum, non sequitur ex necessitate).
Then St. Thomas denies that the proximate end of the first heaven must be the summus deus, as Aristotle had thought. He says: 'For there is both a proximate and a remote end. But it is not necessary that the proximate end of the highest heaven be the supreme immaterial substance, which is the highest god' (Est enim finis et proximus et remotus. Non est autem necessarium quod proximus finis supremi caeli sit suprema substantia immaterialis quae est summus deus).
Rather, it is more probable that, in between the first immaterial substance and the first celestial body, there be many orders of immaterial substances, amongst which the inferior is ordered towards the superior as to an end, and to the lowest of those is ordered the first celestial body as to its proximate end, since there ought to be some sort of proportion in some sort of way between something and its proximate end (sed magis probabile est ut inter primam immaterialem substantiam et corpus caeleste sint multi ordines immaterialium substantiarum, quarum inferior ordinetur ad superiorem sicut ad finem, et ad infimam earum ordinetur corpus caeleste sicut ad finem proximum: oportet enim unamquamque rem esse proportionatam quodam modo suo proximo fini). This means that it isn't probable that a corporeal substance is ordered towards the supreme substance as to its proximate end (Unde propter distantiam maximam primae immaterialis substantiae ad substantiam corpoream quamcumque, non est probabile quod corporalis substantia ordinetur ad supremam substantiam sicut ad proximum finem).
That being so, St. Thomas in this same treatise still has Aristotle as recognising that very first principle which is God. The difference is just that the highest God recognised by Aristotle need not be the immediate mover of the first heaven.
Aristotle had an understanding of the one true God, according to the de Substantiis Separatis
As St. Thomas says in cap. 4, Aristotle posited one order only of things above the souls of the heavens, the first amongst which he posited as the summus deus, while Plato placed the summus deus in the order of forms, such that for him the summus deus was the form of the one and the good:
Aristoteles vero universalia separata non ponens, unum solum ordinem rerum posuit supra caelorum animas; in quorum etiam ordine primum esse posuit summum deum, sicut et Plato summum deum primum esse posuit in ordine specierum, quasi summus deus sit ipsa idea unius et boni.
That St. Thomas thinks that Aristotle had true ideas about the true, one God, is clear from what he says in cap. 3. Plato had argued for a first supreme being who is essentially one and good, through participation of which all inferior substances are one and good, and which is compared to air having light which it participates in from the sun, the cause of its illumination. So also, according to Aristotle, it must be that that which is maximally being and maximally true be the cause of being for everything else:
Primo quidem conveniunt in modo existendi ipsarum. Posuit enim Plato omnes inferiores substantias immateriales esse unum et bonum per participationem primi quod est secundum se unum et bonum; omne autem participans aliquid accipit id quod participat ab eo a quo participat, et quantum ad hoc id a quo participat est causa ipsius: sicut aer habet lumen participatum a sole, quae est causa illuminationis ipsius. Sic igitur secundum Platonem summus deus causa est omnibus immaterialibus substantiis quod unaquaeque earum et unum sit et bonum. Et hoc etiam Aristoteles posuit, quia, ut ipse dicit, necesse est ut id quod est maxime ens et maxime verum sit causa essendi et veritatis omnibus aliis.
Furthermore, both Plato and Aristotle hold that immaterial substances below the supreme one are free from composition of matter and form, but not free from all composition of potency and act. According to Plato, for every thing participating, that which it receives as participated must be the act of the substance participating. This means that aside from the supreme substance which is per se unum and per se bonum, everything else, which participates, must be composed of potency and act. But, it is also necessary to say this according to the judgement of Aristotle. For, Aristotle posits that the notion of true and of good is to be attributed to act; whence, that which is the first truth and the first good must be pure act, whereas whatsoever falls short of this must have some admixture of potency:
Secundo autem conveniunt quantum ad conditionem naturae ipsarum: quia uterque posuit omnes huiusmodi substantias penitus esse a materia immunes, non tamen esse eas immunes a compositione potentiae et actus. Nam omne participans oportet esse compositum ex potentia et actu, id enim quod recipitur ut participatum oportet esse actum ipsius substantiae participantis; et sic, cum omnes substantiae praeter supremam quae est per se unum et per se bonum sint participantes secundum Platonem, necesse est quod omnes sint compositae ex potentia et actu. Quod etiam necesse est dicere secundum sententiam Aristotelis. Ponit enim quod ratio veri et boni attribuitur actui; unde illud quod est primum verum et primum bonum oportet esse actum purum, quaecumque vero ab hoc deficiunt oportet aliquam permixtionem potentiae habere.
Third, Plato and Aristotle have some agreement about Divine Providence. According to Plato, the summus deus, who is ipsum unum and ipsum bonum, on account of the fundamental notion of goodness, must have providence over everything inferior (Tertio vero conveniunt in ratione providentiae. Posuit enim Plato quod summus deus, qui hoc quod est ipsum unum est et ipsum bonum, ex primaeva ratione bonitatis proprium habet ut inferioribus omnibus provideat...). But, according to St. Thomas, Aristotle does not disagree with this. He takes a description from the Metaphysics, which compares the Prime Mover to a general of an army or the master of a household, and that the heavenly beings are to be compared to free children, quick to obey, whereas the earthly beings are to be compared to slaves, deficient in many acts. Now, most scholars do not see this passage as necessarily indicating that Aristotle had in mind something like the notion of Divine Providence known to Christianity. Nevertheless, St. Thomas thought that he did. St, Thomas here says that Aristotle posits one separate good, provident with regard to all things, just like one commander or lord under whom are a diverse order of things. The superior orders (in the heavens) follow the order of perfect providence, whereas the inferior amongst beings receive this order less perfectly and are deficient in many things:
Ab hac etiam providentiae ratione Aristoteles non discordat. Ponit enim unum bonum separatum omnibus providentem sicut unum imperatorem vel dominum sub quo sunt diversi rerum ordines: ita scilicet quod superiores ordines rerum perfecte providentiae ordinem consequuntur, unde nullus defectus in eis invenitur, inferiora vero entium quae minus perfecte providentiae ordinem recipere possunt multis defectibus subiacent; sicut etiam in domo liberi qui perfecte participant regimen patrisfamilias in paucis vel nullis deficiunt, servorum autem actiones in pluribus inveniuntur inordinatae. Unde in inferioribus corporibus defectus proveniunt naturalis ordinis qui in superioribus corporibus nunquam deficere invenitur.
Again, in cap. 4, it is clear that St. Thomas did not think that Aristotle had merely identified a separate substance amongst others, but really the true God. For Aristotle, all the separate substances are both intelligent and intelligible, understanding and understood. The difference is that the summus deus understands not by participation in some higher being which is its perfection, but through its very essence. The inferior separate substances, on the other hand, fall short of the simplicity of the first, and from his supreme perfection, since their act of understanding is only able to be perfected through participation of superior substances:
Hunc autem ordinem Aristoteles posuit utrumque habere, ut scilicet esset intelligens et intellectum: ita scilicet quod summus deus intelligeret non participatione alicuius superioris quod esset eius perfectio, sed per essentiam suam. Et idem aestimavit esse dicendum in ceteris substantiis separatis sub summo deo ordinatis; nisi quod in quantum a simplicitate primi deficiunt et summa perfectione ipsius, eorum intelligere perfici potest per superiorum substantiarum participationem.
Furthermore, in various parts of the Summa Theologiae, motion has a broad metaphysical meaning, which includes the self-motion of the intellect and the will. The intellect insofar as it understand principles, moves itself to understand conclusions. The will insofar as it will an end, moves itself to will means to that end. This is clearly not motion in the strict physical sense as found in Aristotle's Physics.
Conclusion
Strictly speaking, a consideration of physical motion and physical motion alone is not sufficient to come to a God from whom we can draw out all the divine attributes which natural reason is capable of concluding to. However, St. Thomas thought that Aristotle's eternal circular heavenly motion required a being of such power that it must be a completely separate substance. Furthermore, if we were to stop at the immediate mover of the first heaven, as Aristotle did, and declare that to be the Highest Substance, then, with various metaphysical considerations about what the highest separate substance must necessarily be and an argument like the Fourth Way, we can determine that such a being must be God, with the divine attributes St. Thomas knows that God has. However, we can in fact hold that the Highest Substance is not the immediate mover of the first heaven. Nevertheless, in that case, we can simply transfer what Aristotle has said about the mover of the first heaven to that Highest Substance.
1 Paulus, Jean (1933) 'La théorie du premier moteur chez Aristote.' Revue de philosophie, 33: 259-294, 394-424
2 Pegis, Anton C. (1973) 'St. Thomas and the Coherence of the Aristotelian Theology.' Mediaeval Studies 35 (1): 67-117.
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