Aquinas’s Prima Via
In an effort to prove the existence of God, St. Thomas breaks with the tradition before him to come to a proof which is not based on self-evidence, but a logical philosophical demonstration.[1] Using Aristotle’s arguments from both the Physics and the Metaphysics, St. Thomas constructs an argument which synthesizes Aristotle’s proof for an immovable movent, as well as his argument in the Metaphysics concerning an absolutely separate mover. Grounding both St. Thomas’s and Aristotle’s understanding of motion is the notion that motion is an imperfect actuality which brings a thing from F to actuality. It is this definition of motion that allows St. Thomas to set Aristotle’s arguments in a new framework which is only properly understood in light of St. Thomas’s existential metaphysics. However, contemporary critics have argued that St. Thomas’s prima via is not a philosophically sound argument, and that it does not truly transform Aristotle’s proof by using existence as the operative factor. This paper will explain St. Thomas’s version of the prima via, explain how it transforms the Aristotelian arguments, and respond to criticisms of an existential understanding of the prima via with the help of Joseph Owens.
Aquinas’s Prima Via
Of the five ways of the Summa Theologiae, the prima via is the “first and more manifest” (Aquinas quoted in Owens 142). In other words, of all the ways to prove the existence of God, the proof from the actual occurrence of motion is the easiest to assent to, because motion is that by which we explain the sensible world. For example, in the second way Aquinas is able to reason to a first efficient cause in a series of motions, but only by arguing from the “nature of efficient causality,” which is already a more abstract approach than the first way.
The outline of the prima via as found in the Summa Theologiae (1, q.2, a.3) is as follows: (i) It is evident to the senses that some things are in motion, (ii) whatever is in motion is put in motion by another since that which is in motion is in potentiality to that towards which it is motion, (iii) only that which is in a state of actuality can reduce something from potentiality to actuality and motion is this reduction, (iv) it is not possible that the same thing be at once in potentiality and actuality in the same respect (e.g. wood which is potentially and actually hot), (v) it is therefore impossible that a thing should in the same respect and in the same way be both mover and moved (i.e. it cannot move itself), (vi) therefore whatever is in motion is put in motion by another, (vii) if that which puts what is in motion in motion is also in motion, then it must also be put into motion by another, (viii) but this cannot go on forever because then there would be no first mover and therefore no other mover, (ix) therefore it is necessary to arrive at a first mover put in motion by no other and this everyone understands as God.
Aquinas’s Proof in relation to Aristotle’s original arguments
In Aquinas’s restructuring of Aristotle’s arguments, there is a noticeable tendency to defend Aristotle’s arguments against his own conclusion from Book VIII of the Physics. Aquinas’s first mover which everyone understands to be God, is not the same as the first movent of the Physics. For Aristotle, the first movent cannot be understood as the Christian God, because it is material, i.e. physical. After having proved that the first unmoved movent cannot have any magnitude, Aristotle goes on to assert that “the first movent is indivisible and is without parts and without magnitude” (Physics Bk. VIII, ch. 10 267b26).[2] Since the first movent must “occupy” (Physics 267b) the circumference of a sphere, it is quite obvious that this cannot be the non-bodily God of Christianity. For this very reason, Aquinas argues that positing the first movent as a body destroys the truth of the conditional proposition that “if a heavenly body is divided, a part of it will have less power than the whole” (SCG, I, 20, 14). In other words, to posit that the first mover is body, it will follow that a part is of greater power than the whole, since it imparts the power.[3] It is for this reason of proving that the immovable mover is not a body that Aquinas remarks that the first mover does not simply lack a magnitude, but that is has “absolutely no magnitude, existing, as it were, outside of the genus of magnitude” (CAP Book VIII, 1172).
Furthermore, Aquinas’s restructuring of Aristotle’s arguments make it so that those points which do not accord with the Christian God, only do so because they are based off of the eternity of motion. However, for Aquinas motion is not eternal. In fact, according to Aquinas, Aristotle’s reliance on the eternity of motion makes it unnecessary to posit a first principle as innovating principle: “For if it is necessary to posit one first principle on the assumption that the world and motion are eternal, this is much more necessary if the eternity of these things is denied” (CAP Book VIII, 970).
It is clear that it is Aristotle’s reliance on the eternity of motion which makes his conclusion that the first immobile mover is body unwarranted. In Aquinas’s commentary on Aristotle’s Physics, he takes note that Aristotle attributes the eternity of continuous motion both to the immobility of the mover and to its infinite power. If we consider this eternity with respect to the repetition of motion, “it is due to the immobility of the mover” that it is maintained (CAP Book VIII, 1171). However, “the infinite power of the mover is related to the entire eternity or per se infinity of the motion” (CAP Book VIII, 1171). In other words, while the immobility of the first mover ensures eternal continuous motion by virtue of repeated motions, then the entire eternity of the motion is related to infinite power. In this way, Aquinas can deny that the first mover is a body, since for him entire series of infinite movements can have an efficient cause outside of the order of finite bodies. Therefore, Aquinas’s Christian concept of creation ex nihilo allows for him to deny that the first efficient must be of the same causal order as all finite bodies.
This understanding of an efficient cause outside the order of the per se infinite series of finite bodies in motion is central to understanding Aquinas’s proof as having an existential operative factor. This reformulation of Aristotle within the context of an existential metaphysic is obvious even in Aquinas’s commentary on the Physics. In Book VIII, after Aristotle states that “the existence of motion is asserted by all who have anything to say about nature,” Aquinas comments, “(here Aristotle) applies the common consideration of motion to the existence which it has in things. Therefore, one might say that in this consideration one must ask whether motion has existence in things before one asks whether motion is eternal […]” (CAP Book VIII, 967). In other words, Aristotle’s considerations of motion take on existential implications as soon as they are concerned with real objects in the world. For Aquinas, as will be shown below, this will mean that when motion is taken in concreto, i.e. when it is considered as the movement of that which has an essence, the efficient cause of all motion is also that cause which actuates a nature and gives a thing its being.
Contemporary criticism of the prima via
When Anthony Kenny denies that the first premise of the prima via has existential metaphysical implications (or, as he puts it, involves “occult metaphysical transitions” [10-11]), he is considering the prima via in a context in which the arguments do not necessarily lead to God as first cause. That is, from Aquinas’s commentary on the Physics, and the way that he has reformulated the Aristotelian arguments, it is evident that Aquinas’s arguments are meant to have different metaphysical implications as those of Aristotle. Aquinas is able to argue towards an immaterial first efficient cause outside the per se infinite order of finite motions because of his denial of the eternity of motion.[4] Therefore, all his uses of Aristotle will be of a conditional nature, i.e. if continuous motion were eternal, then it would be necessary to posit a non-divisible immobile movent at the circumference of a heavenly sphere. So to understand the prima via is to understand the way in which a first mover can impart motion, yet be outside the causal order of all finite things, yet still have infinite power which is not restricted to the impediments of occupying a finite space, i.e. the first mover must be “outside the genus of magnitude.”
Kenny argues against Owens, who maintains that the Aristotelian argument for motion is analyzed ultimately in terms of existential act’ in Aquinas, by saying that “the texts…from St. Thomas do not seem to support the nonsensical view that when you have explained a particular motion at a particular time you have to explain also the occurrence of the motion” (11). However, his disagreement with Owens seems to stem from a misunderstanding of the existential act (esse), which Kenny takes to mean “the actual occurrence of a motion, this being taken to be something different from the motion occurring” (11).
To understand esse we must understand that for Aquinas motion is “essentially imperfect” on the metaphysical level (Owens 147). For both Aristotle and Aquinas motion is the fulfillment of what is potential with respect to some actuality.[5] However, we also learn from Aristotle that that which is in the process of motion is fully real: “It is the fulfillment of what is potential when it is already fully real and operates not of itself but as movable, that is motion” (Physics 201a28). That which is in motion, i.e. moving, is already ‘fully real,’ but in moving is also that which is potential. To be potential is to be potential in some respect to what is actual, which is why that which is moving is doing so ‘not of itself.’ Motion is therefore an imperfect actuality, because even though it is fully real, i.e. it has an actuality in reality, it is still lacking because as movable it is not fully actual with respect to that which it is changing. Also, since change can only take place by virtue of two termini, i.e. that from which and to which a thing changes, and since only that which is actual can cause motion,[6] every motion will have a two-fold actuality. Therefore, every motion implies an “imperfect actuality in which motion itself consists, and the further terminal actuality that the very nature of motion implies” (172).
We can now understand what Owens means when he says that “the fact that some things are being moved in the sensible world means that they have the existential actuality (esse) of motion and by its means are in the process towards the further existential actuality (esse) of its terminus” (174). So when Kenny states that it is “nonsensical” to maintain “the actual occurrence of a motion (for him esse)” as different from “the motion occurring” (11), he is within the same Aristotelian framework which Aquinas is denying. In other words, it is not “nonsensical” to maintain that there is the existence of a motion (since it is fully real, yet imperfectly actual), as well as an existence of the terms of the motion. For Aquinas, form is not able to account for efficient causality, e.g. it cannot explain the new act which actuates a formal act within equivocal agents. So for Aquinas, it would make sound sense to say that in sensible motion there is the motion occurring (formal causality) and the actual occurrence of the motion (efficient causality).
To properly understand how Aquinas is able to make this distinction, it is important to see how Aquinas transforms the Aristotelian understanding of being (ousia), especially as it relates to the subjects of motion. For Aristotle, of the three kinds of mutation (Physics 225a4), only one can be understood as change: mutation from subject to subject (Physics 225b1). Also, for Aristotle subject is defined as that which “is affirmatively expressed (225a7),” and for this reason change cannot occur in Substance. That is to say, substance in both its senses, (i) ultimate substratum which is predicated of and (ii) the separable form of a thing which is a ‘this’ (Metaphysics 1017b23), cannot be a subject because non-accidental change can only be found in contraries. The predicate-less Substance cannot be contrary to anything else, since to be contrary is to be contrary with respect to an attribute. For example, the contrary of ‘human-being’ cannot be any other substance, and the only conceivable negative change would really only be a change to a contradictory (non-being), and this cannot be motion (Physics 225a25).
To say that motion can only occur from subject to subject, in the Thomistic Metaphysics, is to say that motion can only occur if a thing has an essence. For Aristotle, “that which is without qualification ‘not-so-and-so (Physics 225a24)’” cannot be in motion. For Thomas, only the subject of being can be said to have an essence. Also, for him “a necessary requirement for essence is a positive status in reality (Owens 80).” In other words, we can form affirmative propositions about things which do not have a positive status in reality, e.g. negations and privations, but the being expressed in such a proposition would be different than the subject of being which can divided into the ten categories (Owens 80, these are the two senses of ens per se). However, essence generally “will be that which places anything whatsoever in a category” (Owens 81). So, that which is without qualification ‘not-so-and-so,’ is also that which is without an essence, because to have an essence is to be determined and placeable in one of the ten categories. In other words, only that which has an essence can be involved in motion.
The essence or nature of a thing is placed in the ten categories regardless of whether it is considered as in actuality or as in potentiality. However, that which is considered as actual “would be considered along with its being,” while that which is considered as potential “would be taken without the act and so as just one constituent of the composite” (Owens 83). This allows Aquinas to comment (see above) that Aristotle is only concerned with the existence of motion in things once he stops being concerned with it only generally; because only when concerned with concrete being do we need to consider a proper act of being. The prima via, therefore, cannot work when motion is considered apart from the actual moving and being moved of the subjects of motion.
An essence is “that by which a thing is denominated a being” (83), and is both form and matter. Only the form, however, can serve as “the formal cause and denominating principle.” In relation to essence, being (esse) can only be considered as outside the essence of a creature and therefore the being of a creature must be considered as an accident (90). However, with respect to created things, esse “inheres in essence and adheres to essence, in the manner of an accident”[7] (91). However, since without being there would be no predicates and no determination of an essence, esse must be prior to essence. In totality, “created essence is of its own nature an order to being,[8] and so far as it is concerned being is essential to it…(however) in order to be, it also has to be produced efficiently by something other than itself, and from that viewpoint its being is accidental to it” (Owens 95). In the case of motion, therefore, Aristotle’s entire argument holds because it is concerned only with formal causality. However, the real efficient cause of the entire formal causal chain must be a pure act of being (esse) which is not in potentiality to anything. Therefore, the conclusion of Aquinas’s prima via leads to the existence of a “prime[9] unmoved mover” (SCG, 1, ch. 13, ¶ 3, emphasis added); i.e. a mover which cannot be moved precisely because it is already fully act.
An essence is “that by which a thing is denominated a being” (83), and is both form and matter. Only the form, however, can serve as “the formal cause and denominating principle.” In relation to essence, being (esse) can only be considered as outside the essence of a creature and therefore the being of a creature must be considered as an accident (90). However, with respect to created things, esse “inheres in essence and adheres to essence, in the manner of an accident”[7] (91). However, since without being there would be no predicates and no determination of an essence, esse must be prior to essence. In totality, “created essence is of its own nature an order to being,[8] and so far as it is concerned being is essential to it…(however) in order to be, it also has to be produced efficiently by something other than itself, and from that viewpoint its being is accidental to it” (Owens 95). In the case of motion, therefore, Aristotle’s entire argument holds because it is concerned only with formal causality. However, the real efficient cause of the entire formal causal chain must be a pure act of being (esse) which is not in potentiality to anything. Therefore, the conclusion of Aquinas’s prima via leads to the existence of a “prime[9] unmoved mover” (SCG, 1, ch. 13, ¶ 3, emphasis added); i.e. a mover which cannot be moved precisely because it is already fully act.
Thus, when Kenny argues that it is nonsense that every potentiality of a creature in its tendency to actual motion “needs to be actualized by the immediate action of the Creator” (18), he is confusing formal causality with efficient causality. The Creator need not actualize the potentiality of a creature to motion, he need only actualize the essence of the creature as efficient cause, and this essence will itself act as formal cause in series of finite motions.
When Kenny argues against the principle that to bring something from potentiality to actuality a thing must itself be in actuality, he states that the “falsifications of the principle are fatal to the argument” (22). His example is local motion: according to this principle the only way a projectile can by moved to B, is by something which is already at B.
[1] The instances of the proof concerned here are those found in the Summa Contra Gentiles, Book 1, Ch. 13., and the Summa Theologiae, 1, q.2, a.3.
[2] According to Aristotle, “everything that changes must be divisible;” (Physics 234b10) this is because every change is from something to something. If a thing changes from something to something, then it must not be changing when itself and all its parts are either at the starting-point or end-point of change. In other words, there must be a part already at the end-point which serves as end cause to the process of change. However, the thing as a whole cannot be in either extreme or in neither, therefore it is evident “that everything that changes must be divisible,” (Physics 234b) and since motion is a species of change, this must also hold for motion.
[3] When defending the two main propositions of the prima via, “that everything that is moved is moved by another, and that in movers and tings moved one cannot proceed to infinity” (SCG, I, ch. 13, ¶ 4), Aquinas extracts arguments from book VI of Aristotle’s Physics (SCG, 1, ch. 13, ¶ 5-6) to show that a self-moving being is impossible because of the divisibility of its parts. However, it is important to note that Aquinas states that “the moving of the divisible itself, like its being [sicut et ejus esse], depends on its parts; it cannot therefore move itself primarily and through itself.”This is important because it shows that the efficient cause of motion is outside the parts of that which is moved, and also that that which is moved has a being dependent on its parts. As the divisible will have an efficient causality of motion outside of itself, so too will the cause of its being be outside of it.
[4] It is for this reason that Owens can claim that St. Thomas “has clearly shifted the starting point of the demonstration from the Aristotelian eternity of motion to the esse of motion” (148).
[6] For Aristotle, motion is the fulfillment of what is in potentiality, “by the action of that which has the power of causing motion” (Physics 202a12). Also, “the actuality of that which has the power of causing motion is not other than the actuality of the movable, for it must be the fulfillment of both. A thing is capable of causing motion because it can do this, it is a mover because it actually does it” (Physics 202a14-17). That which is moving something is doing it actually (in process) by virtue of its own actuality, and therefore, also the actuality of that which is in potentiality. Owens, speaking about the virtual acts of Dun Scotus, states that the problem of this conception of actuality is that there explanation of “the new act of existing that actuates a formal act which before was found only virtually in its cause” (165). In other words, with respect to equivocal agents, a cause must actuate a potentiality by virtue of a form which is not actuated itself in the mover, but is there only as a virtual act.
[7] Since the act of being cannot enter into the definition of a thing, i.e. it cannot place it in one of the ten categories, it must be accidental to it: “[…] only that which does not enter the definition of a thing seems to be outside its essence or quiddity…but it is only the accidents of a thing that do not fall in the definition” (SCG, 1, ch. 21, ¶ 3)
[8] I other words, created essence must be in potency to the act of being: “Being, furthermore, is the name of an act, for a thing is not said to be because it is in potency but because it is in act. Everything, however, that has an act diverse from it is related to that act as potency to act; for potency and act are said relatively to one another” (SCG, 1, ch. 22, ¶ 7).
[9] Since it is prime, and it is a being, this must also mean that the unmoved mover is a primary being, i.e. a substance: “[…]that which ‘is’ primarily is the ‘what’, which indicates the substance of the thing” (Metaphysics Bk VII, 1 1028a14). For this reason, God is Ipsum Esse Subsistens.
