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The situation is very different as regards the first two arguments in SCG's chapter 13. I'll label them G1 and G2. They are very nearly equally long, and each of them, with its supporting arguments, is more than ten times longer
than any of the last three SCG arguments.
15 G1 takes 170 columnar lines in the Marietti edn. of SCG; G2, 174. (Sects. 109-12 of 1.13 contain a special appraisal of G2.) The third argument takes 17 lines, the fourth, 13, and the fifth, 14.
Aquinas introduces G1 and G2 as a thematically linked pair: 'But first we will present arguments by means of which Aristotle sets about proving that God exists. He undertakes to prove it on the basis of motion, in two ways' (13.82).
As for Aquinas's attributing G1 and G2 to Aristotle, it's certainly true that the appropriate passages in Aristotle's Physics and Metaphysics prefigure these arguments to varying degrees, sometimes in detail. But Aquinas's reworking and endorsing of them as arguments for the existence of God make him directly responsible for G1 and G2, and I'll treat them as his arguments
without feeling obliged to comment on their Aristotelian background.
16 For helpful commentary of that sort see e.g. Gerson 1990b.
I will, however, make use of the helpful parallel passages in Aquinas's
commentaries on the Physics
17 See also van Steenberghen 1971.
and the Metaphysics,
18 See also van Steenberghen 1974.
both of which he seems to have been writing within six years of finishing SCG (see Appendix I).
As for Aquinas's identifying 'motion' as the basis of these arguments, his use of the Latin word motus in them parallels Aristotle's broad, generic use of the Greek word kinesis to mean either change of location (local motion) or qualitative change (alteration) or quantitative change (increase or decrease). In this discussion I'll continue to use the words 'motion', 'move', 'mover', and
so on, taking that broad, generic interpretation of them for granted.
19 G1 is presented by Aquinas as if local motion alone might be basis enough for the argument, while in STs closely similar First Way his single paradigm of motion is a case of alteration. In G2, on the other hand, a consideration of all the genera and species of motion is essential to the structure of the argument, as we'll see.
Aquinas says that both G1 and G2 proceed 'on the basis of motion' (ex parte motus), the very words with which he later characterizes ST's First Way. Do both G1 and G2 correspond to the First Way, then? No. The correspondence between the First Way and the main argument of G1 is quite close. In each of them the end p.61
© Copyright Oxford University Press, 2006. All Rights Reserved same two premisses require support. G1 provides the support in six separate, detailed arguments (three for each of the dangling premisses); the First Way provides it succinctly in two sub-arguments incorporated into the main argument. As Aquinas's apparent favourite among the Five Ways, the First Way, the manifestior via, has received a great deal of critical attention. Gl, its more complicated ancestor, has been comparatively neglected; but a recent article by Scott MacDonald (1991a) does a beautiful job of examining Gl and the First Way together and, more important, of answering the well-known objections to this sort of argument from motion. For the practical purpose of starting natural theology with a good argument for the existence of God along the lines provided in SCG, I could simply present Gl as analysed and defended by MacDonald. But, partly because he has already ably done that work on Gl, I want to focus on the almost totally neglected and misconstrued G2. MacDonald's main thesis is that the argument from motion which Aquinas develops in Gl and in the First Way is incomplete in itself, but valid if completed by certain modal considerations, and that Aquinas himself realized this. The requisite modal considerations, MacDonald maintains, are supplied for the First Way in the Third Way (1991a: 154). In an allusion to G2, he suggests that it may have been intended to play a
corresponding role in support of Gl.
20 MacDonald 1991a: 152: 'In his presentation of the second "Aristotelian" proof [G2], he [Aquinas] acknowledges that the claim that there is a primary mover that is not moved by anything exterior to it does not entail that there is a primary mover that is completely unmovable [as Gl concludes], ... It seems to me plausible ... to suppose that he was aware of the parasitic nature of the first "Aristotelian" proof and that he left it unremarked in view of the forthcoming supplementary discussion.'
Perhaps he's right about that, but I want to consider G2 on its own as nearly as possible.
The principal difference between Gl and the First Way is that Gl offers alternative supporting arguments and spells out everything in more detail. It is more complex than the First Way, but only extrinsically and accidentally. G2, on the other hand, is intrinsically and substantively a more complex argument from motion than either the First Way or Gl, and G2 has no
counterpart among the Five Ways.
21 G2 is altogether the most complex of all Aquinas's arguments for God's existence. Its complexity appears to have been the principal consideration that led van Steenberghen, astonishingly, to omit any detailed treatment of it from his big book devoted entirely to Aquinas's arguments for God's existence, where he characterizes it as a complicated, scientifically antiquated reprise of Gl—too complicated in its structure and implausible in its assumptions to be worth examining closely: 'Une fois de plus la preuve est développée avec un luxe de considérations qui se situent au niveau de la science aristotélicienne dans ses éléments les plus caducs. Il faudrait des pages nombreuses pour analyser et critiquer en détail cette démonstration, sans profit notable pour le lecteur' (van Steenberghen 1980: 117-18; emphasis added).
Despite Aquinas's clearly treating it as a second end p.62
argument in chapter 13, some have taken G2 to be simply continuous with
Gl, forming one huge argument from motion.
22 See e.g. Baisnee 1952; also van Steenberghen 1966: 120; also Martin 1988: 99-100. Martin, indeed, seems to think that all of SCG 1.13 constitutes one single argument.
But because, as the reader may have noticed, no counterpart for the Third Way appears among the four other arguments of chapter 13, it has sometimes been supposed that G2 must fill that particular gap—not merely relating to Gl as MacDonald claims that the Third Way relates to the First, but prefiguring the Third Way itself. In an article on Aquinas's arguments from motion the Polish logician Jan Salamucha presents an instructively
mistaken version of this view of G2.
23 Salamucha 1958; repr. in Kenny 1969.
He writes: The second proof ex motu given in the Summa contra Gentiles, is connected with that of ex contingentia mundi [the Third Way], For this reason, St. Thomas himself is not satisfied with this proof and closed it with the remark, Praedictos autem processus duo videntur infirmare . . . ["Two things appear to weaken the lines of reasoning we have been considering . . . "]. He then gives explanations stressing the weak points of the proof. It is possible that later this second proof ex motu was reformulated, elaborated
and presented in the Summa Theologiae as the proof ex contingentia.'
24 Salamucha 1958, Kenny 1969: 177; cf. MacDonald 1991a: 149 n. 56.
G2 does resemble the Third Way in its concern with modalities, but that resemblance is superficial in view of the essential differences between the two arguments. Most notably, the Third Way, like the First Way and Gl, must take on the notoriously hard job of trying to block an infinite regress of moved movers, while G2 not only tolerates but systematically incorporates
such a regress.
25 SCG contains another argument that has been described as prefiguring the Third Way very closely, one that appears in a later chapter of SCG in a version designed to serve as an argument for God's eternality (15.124). Van Steenberghen argues (1966: 126-7) that the Third Way is unsatisfactory as it stands, but can be improved by revisions drawn from this SCG argument, which he describes as 'the more satisfactory formula' of the argument from contingency (p. 149). The argument in 15.124 will be considered in Ch. Three, but not as a version of the Third Way.
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What Salamucha takes to be 'explanations stressing the weak points' of G2 are actually Aquinas's reassurances regarding two aspects of it that someone might mistakenly suppose to be grounds for objecting to it. In examining G2, we'll see reasons why Aquinas might very well have become dissatisfied with it eventually; but he certainly shows no dissatisfaction with it in SCG. On the contrary, he promotes G2 as being in at least one respect 'the most efficacious way (via efficacissima) of proving that God exists' (13.110). In his final appraisal of G2, the first of the two aspects of it that Aquinas says 'appear to weaken' it is the fact that it is constructed 'on the basis of
[Aristotle's] hypothesis of the eternity [i.e. the beginninglessness] of motion, which among Catholics is taken to be false'. However, he points out, 'the most efficacious way of proving that God exists is on the hypothesis of an eternal [i.e. beginningless] world, [just because] on that hypothesis it seems less evident that God exists. For if the world and motion did have a first beginning, then, plainly, we must posit some cause that produces the world and motion to begin with. For everything that comes into existence for the first time must get its start from some originator, because nothing brings itself from potentiality to actuality, or from non-existence to existence'
26 Cf. In Phys. VIII: LI.970: This way of proving that there is a first source [viz. on the hypothesis of the beginninglessness of motion] is the most efficacious way, which cannot be resisted. For if it is necessary to suppose that there is one first source in case the world and motion exist sempiternally, it is much more so if their sempiternity is ruled out, since it is evident that everything that is new needs an originating source. Therefore, it is only if things exist from eternity that it could seem unnecessary to posit a first source. And so if it follows that a first source exists even on that hypothesis, it is shown to be altogether necessary that a first source exists.' For this passage and other relevant data about the text of Aquinas's appraisal of G2, see the note to 13.110 in the Marietti edn. of SCG (vol. II, app. I, p. 286).
G2, then, seems to have been designed to show that there must be a being whose existence and nature account for the world's existence, even when
the world is viewed as having existed always.
27 The second of the two features of G2 that appear to weaken it is discussed in sect. 5, stage III, below.
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