William M. Briggs

Statistician to the Stars!

Category: SAMT (page 30 of 32)

A tour through Saint Thomas Aquinas’s Summa Contra Gentiles.

Summary Against Modern Thought: The Last Movement

This may be proved in three ways. The first...

This may be proved in three ways. The first…

See the first post in this series for an explanation and guide of our tour of Summa Contra Gentiles.

Previous post.

Recall that the First Way has already been done. Meaning we already have one proof for God’s existence. This is the second, and the good news is that most of our terminology has already been introduced. A lot to do today, but the good news is that this is the last of Chapter 13! But these proofs are all we have. We don’t yet know anything about God except that He’s the Unmoved Mover, the Unchanging Changer. What can that mean? That’s coming.

Chapter 13: Arguments in proof of God’s existence

18 Again, if any two things are found accidentallyi united in a certain subject, and one of them is to be found without the other, it is probable that the latter can be found without the former: thus if white and musical are found in Socrates, and musical without white is found in Plato, it is probable that it is possible to find white without musical in some subject.

Accordingly if mover and moved be united together in some subject accidentally, and it be found that a certain thing is moved without its being a mover, it is probable that a mover is to be found that is not moved. Nor can one urge against this the case of two things one of which depends on the other; because those in question are united not per se but accidentally.

If, however, the aforesaid proposition is true in itself, again there follows something impossible or unfitting. For the mover must needs be moved either by the same kind of movement or by another kind. If by the same kind, it follows that whatever causes alteration must itself be altered, and furthermore that the healer must be healed, that the teacher must be taught, and in respect of the same science. But this is impossible: for the teacher must needs have science, while the learner must needs not have it, and thus the same will be both possessed and not possessed by the same, which is impossible.ii

And if it be moved by another kind of movement, so that, to wit, that which causes alteration be moved in respect of place, and that which moves in respect of place be increased, and so on, it will follow that we cannot go on indefinitely, since the genera and species of movement are finite in number.iii And thus there will be some first mover that is not moved by another. Unless, perchance, someone say that a recurrence takes place, in this way, that when all the genera and species of movement have been exhausted, a return must be made to the first; for instance, if that which moves in respect of place be altered, and that which causes alteration be increased, then again that which is increased be moved in respect of place. But the consequence of this will be the same as before; namely, that which moves by one kind of movement is itself moved by the same kind, not immediately indeed but mediately.iv It remains therefore that we must needs postulate some first mover that is not moved by anything outside itself.

19 Since however, given that there is a first mover that is not moved by anything outside itself,v it does not follow that it is absolutely immovable, Aristotle proceeds further, saying that this may happen in two ways. First, so that this first mover is absolutely immovable. And if this be granted, our point is established, namely that there is a first immovable mover. Secondly, that this first mover is moved by itself. And this seems probable: because what is of itself is always prior to what is of another: wherefore also in things moved, it is logical that what is moved first is moved by itself and not by another.

20 But, if this be granted, the same consequence follows.[18] For it cannot be said that the whole of that which moves itself is moved by its whole self, because then the absurd consequences mentioned above would follow, namely that a person might teach and be taught at the same time, and in like manner as to other kinds of movement; and again that a thing would be at the same time in act and in potentiality, since a mover, as such, is in act, while that which is moved is in potentiality.vi It remains, therefore, that one part thereof is mover only, and the other part moved. And thus we have the same conclusion as before, namely that there is something that moves and is itself immovable.

21 And it cannot be said that both parts are moved, so that one is moved by the other; nor that one part moves both itself and the other; nor that the whole moves a part; nor that part moves the whole, since the above absurdities would follow, namely that something would both move and be moved by the same kind of movement, and that it would be at the same time in potentiality and in act, and moreover that the whole would move itself not primarily but by reason of its part. It remains, therefore, that in that which moves itself, one part must be immovable, and must move the other part.

22 Since, however, in those things among us which move themselves, namely animals, the part which moves, namely the soul, though immovable of itself, is nevertheless moved accidentally, he goes on to show that in the first mover, the part which moves is not moved neither of itself nor accidentally.[19]vii

23 For in those things which among us move themselves, namely animals, since they are corruptible, the part which moves is moved accidentally. Now those corruptible things which move themselves must needs be reducible to some first self-mover that is everlasting. Therefore that which moves itself must have a mover, which is moved neither of itself nor accidentally.

24 It is clear that, in accordance with his hypothesis, some self-mover must be everlasting. For if, as he supposes, movement is everlasting, the production of these self-movers that are subject to generation and corruption must be everlasting. But no one of these self-movers, since it does not always exist, can be the cause of this everlastingness. Nor can all of them together, both because they would be infinite, and because they do not exist all together. It follows therefore that there must be an everlasting self-mover, that causes the everlastingness of generation in these lower self-movers. And thus its mover is not moved, neither of itself nor accidentally.

Again, we observe that in self-movers some begin to be moved anew on account of some movement whereby the animal is not moved by itself, for instance by the digestion of food or a change in the atmosphere: by which movement the mover that moves itself is moved accidentally. Whence we may gather that no self-mover, whose mover is moved per se or accidentally, is always moved. But the first self-mover is always in motion, else movement could not be everlasting, since every other movement is caused by the movement of the first self-mover. It follows therefore that the first self-mover is moved by a mover who is not moved, neither per se nor accidentally…viii

30 The Philosopher proceeds in a different way in 2 Metaph. to show that it is impossible to proceed to infinity in efficient causes, and that we must come to one first cause, and this we call God. This is how he proceeds. In all efficient causes following in order, the first is the cause of the intermediate cause, and the intermediate is the cause of the ultimate, whether the intermediate be one or several. Now if the cause be removed, that which it causes is removed. Therefore if we remove the first the intermediate cannot be a cause. But if we go on to infinity in efficient causes, no cause will be first. Therefore all the others which are intermediate will be removed. Now this is clearly false. Therefore we must suppose the existence of a first efficient cause: and this is God.ix

31 Another reason can be drawn from the words of Aristotle. For in 2 Metaph.[22] he shows that those things which excel as true excel as beings: and in 4 Metaph.[23] he shows that there is something supremely true, from the fact that we see that of two false things one is falser than the other, wherefore it follows that one also is truer than the other. Now this is by reason of approximation to that which is simply and supremely true. Wherefore we may further conclude that there is something that is supremely being. And this we call God.x

32 Another argument in support of this conclusion is adduced by Damascene[24] from the government of things: and the same reasoning is indicated by the Commentator in 2 Phys.[25] It runs as follows. It is impossible for contrary and discordant things to accord in one order always or frequently except by someone’s governance, whereby each and all are made to tend to a definite end. Now we see that in the world things of different natures accord in one order, not seldom and fortuitously, but always or for the most part. Therefore it follows that there is someone by whose providence the world is governed. And this we God.xi


iA circle can be accidentally red or yellow and still be a circle, etc. A thing is not defined by its accidents.

iiAquinas created this argument in ignorance of our modern educational system, of course. But he’s still right.

iiiYou can change quantity, mass, color, place, and the like, but there are not an infinite number of changeable qualities.

ivDon’t loose sight of the main example, the stone moved by the stick moved by the arm moved by the muscles, etc., all in the here and now. This movement cannot be circularly caused.

vWe’re starting to hone in on (but have not reached) the idea that there can be only one Unmoved Mover, and not an assemblage of them. Not gods, but God.

viYou cannot potentially and actually be in Cleveland simultaneously. Aquinas is speaking ontologically, not epistemologically. And this reminds me that we have to, sometime soon, introduce Jaki’s criticisms of complementarity.

viiWe’ll also do this more later. But, for now, the soul of the animal is its form. Things are composed of forms and substances or matter. Clay, a substance, can be in the form of an ashtray (eek!) or (say) a model car. Speaking loosely, and later correctly, the soul animates the substance. The souls of plants are lesser than the souls of animals, which in turn are lesser than the souls of men. Like I said, this is only a crude introduction. Let’s stick here to the argument of movement, else we will be arguing that of which we have incomplete information.

viiiYou may feel buried after these last two paragraphs. Slow reading is in order. Again, Aquinas is leading us to why there can be only one Unmoved Mover. There’s no getting around that this last proof is rather dry—I even leave out some discussion about movement of heavenly bodies—but it dots all the Js and crosses all the Xs.

ixHere it is in a compact form! This is the elevator proof. Pretty, too.

xI don’t think Aquinas expected this snippet to be convincing in itself, but included it as an augment to main argument. Here’s a good article from Swinburne on the argument from the beauty of design, and another by Williams on beauty.

xiAnd this sketch is cruder still. It’s doubtful that it, in this telegraphic form, would convince any moderns. I’m not expert enough in Medieval history to know why Aquinas included it, which audience he had in mind.

Hooray! We are finally done with Chapter 13! But not entirely done with motion.

[18] 8 Phys., l.c.
[19] 8 Phys. vi.
[22] D. 1a. i. 5.
[23] D. 3. iv. 27, 28.
[24] De Fide Orth. i. 3.
[25] Text 75.

Summary Against Modern Thought: Contingency & Necessity

This may be proved in three ways. The first...

This may be proved in three ways. The first…

See the first post in this series for an explanation and guide of our tour of Summa Contra Gentiles.

Previous post.

The First Way is in the bag. And now we continue, fresh as it were, with the Second Way. But since this introduces what are unfamiliar concepts to some, we again slow down. But have no fear: after this chapter, we can again speed up, because most of the terms will by then be familiar.

Chapter 13: Arguments in proof of God’s existence

16 We have thus clearly proved both statements which were supposed in the first process of demonstration whereby Aristotle proved the existence of a first immovable mover.viii

17 The second[16] way is as follows. If every mover is moved, this statement is true either in itself or accidentally. If accidentally, it follows that it is not necessary: for that which is accidentally true is not necessary.i Therefore it is a contingent proposition that no mover is moved.ii But if a mover be not moved, it does not move, as the opponent asserts. Therefore it is contingent that nothing is moved, since, if nothing moves, nothing is moved. Now Aristotle holds this to be impossible,[17] namely, that at any time there be no movement.iii Therefore the first proposition was not contingent, because a false impossibility does not follow from a false contingency. And therefore this proposition, Every mover is moved by another, was not accidentally true.iv


iMost things you know are contingently true. It is true (supposing) that your car is in your driveway, but only because you bought a car and parked it there. The universe did not require you to buy this car. Not everybody has a car (Yours Truly does not). Propositions which are contingently true can be imagined false. I can easily imagine you too do not have car. No rules of logic would be violated were that to be so.

A necessary truth is that which cannot be other than true. A necessary truth cannot be imagined false. Here is a necessary truth: “A thing cannot both exist and not exist simultaneously.” It is impossible to imagine, or more properly to think of, a thing existing and not existing at the same time. Logic cannot be violated.

When speaking of contingency, some speak of “possible worlds”, as if the world in which you do not own a car is, somehow, brought into existence by your imagining you do not have a car; a sort of milky idealism. Or that this “possible world”, simply because it can exist, actually exists; perhaps part of a multiverse or one of the “many worlds” where all events occur.

But this thinking mixes up the existence of a thing with the knowledge of the thing. Ontology is not epistemology. Things can exist without your, or anybody’s, knowledge. And you can have knowledge (or rather can think) of things that do not exist, like conservative sociologists or the Starship Enterprise. The latter does not come into existence just because it can be imagined.

Now some say of necessity that nothing occurs “at random” or “randomly”. But this is to make the same mistake. Randomness isn’t a thing. It therefore cannot be a cause. Best way to think of this is to substitute “ignorance” every time you see random. If the sentence is still sensible, then the author has a proper understanding; if not, then not.

iiIf it is only contingently true that “no mover is moved”, it can be imagined that “it is false that no mover is moved.” And you have to love the next two sentences.

iiiSome highlights from Aristotle (following the footnote):

…Now the existence of motion is asserted by all who have anything to say about nature, because they all concern themselves with the construction of the world and study the question of becoming and perishing, which processes could not come about without the existence of motion.

It is not always asserted by some readers here, but let that pass. Continuing, we see that talk of “infinite possible worlds” is not a new invention. (I added extra paragraphs for readability.)

But those who say that there is an infinite number of worlds, some of which are in process of becoming while others are in process of perishing, assert that there is always motion (for these processes of becoming and perishing of the worlds necessarily involve motion), whereas those who hold that there is only one world, whether everlasting or not, make corresponding assumptions in regard to motion. If then it is possible that at any time nothing should be in motion, this must come about in one of two ways…

…Motion, we say, is the fulfilment of the movable in so far as it is movable. Each kind of motion, therefore, necessarily involves the presence of the things that are capable of that motion. In fact, even apart from the definition of motion, every one would admit that in each kind of motion it is that which is capable of that motion that is in motion: thus it is that which is capable of alteration that is altered, and that which is capable of local change that is in locomotion: and so there must be something capable of being burned before there can be a process of being burned, and something capable of burning before there can be a process of burning.

Moreover, these things also must either have a beginning before which they had no being, or they must be eternal. Now if there was a becoming of every movable thing, it follows that before the motion in question another change or motion must have taken place in which that which was capable of being moved or of causing motion had its becoming.

To suppose, on the other hand, that these things were in being throughout all previous time without there being any motion appears unreasonable on a moment’s thought, and still more unreasonable, we shall find, on further consideration. For if we are to say that, while there are on the one hand things that are movable, and on the other hand things that are motive, there is a time when there is a first movent and a first moved, and another time when there is no such thing but only something that is at rest, then this thing that is at rest must previously have been in process of change: for there must have been some cause of its rest, rest being the privation of motion…

We went as as this for two reasons: (1) Aquinas was not pulling his assertion about Aristotle out of thin air, and that Aristotle’s assertion is true, and (2) for the phrase “rest being the privation of motion”. This is a tease, but the concept of privation will become important for us. For instance, evil, as it will turn out, is privation of the good. But let’s not get distracted by this today.

ivSince we’ve already done a lot, without really have done much, we leave this phrase hanging in the air, as it were. We’ll pick up with it again next week. Very little was proved this week, except Aristotle’s small proposition.

Next installment.

[16] [8 Phys. v.] [17] 8 Phys. i.

Summary Against Modern Thought: Non-existence Of Infinite Causal Chains

This may be proved in three ways. The first...

This may be proved in three ways. The first…

See the first post in this series for an explanation and guide of our tour of Summa Contra Gentiles.

Previous post.

Here’s what was proved so far: (1) that some things move and others change, and that (2) whatever is in the process of being moved or being changed is being moved or changed by another. Utterly unremarkable assertions; but both the backbone of science, even though some scientists pretend to be skeptical of causality. There is a world, nay a universe, of difference between our knowledge of a cause and of the existence of a cause. Poor Jaki spent his career reminding people of Heisenberg’s fallacy of equivocation. “Poor” because, for whatever reason, people cannot keep in mind the difference between epistemology and ontology. Once more I beg you to read the stone being moved by the stick being moved by the arm being moved by the muscles etc. example. Today we reach the end of the First Way. Next week we begin the Second way.

Chapter 13: Arguments in proof of God’s existence

4 This argument contains two propositions that need to be proved: namely that whatever is in motion is moved by another, and that it is not possible to proceed to infinity in movers and things moved…

11 He proves the other proposition, namely that it is impossible to proceed to infinity in movers and things moved, by three arguments.i

12 The first[10] of these is as follows. If one were to proceed to infinity in movers and things moved, all this infinite number of things would necessarily be bodies, since whatever is moved is divisible and corporeal, as is proved in 6 Phys.[11]ii Now every body that moves through being moved is moved at the same time as it moves.iii Therefore all this infinite number of things are moved at the same time as one of them is moved. But one of them, since it is finite, is moved in a finite time. Therefore all this infinite number of things are moved in a finite time. But this is impossible. Therefore it is impossible to proceed to infinity in movers and things moved.iv

13 That it is impossible for the aforesaid infinite number of things to be moved in a finite time, he proves thus.[12] Mover and moved must needs be simultaneous; and he proves this by induction from each species of movement. But bodies cannot be simultaneous except by continuity or contact. Wherefore since all the aforesaid movers and things moved are bodies, as proved, they must needs be as one movable thing through their continuity or contact. And thus one infinite thing would be moved in a finite time, which is shown to be impossible in 6 Phys.[13]v

14 The second argument[14] in proof of the same statement is as follows. In an ordinate series of movers and things moved, where namely throughout the series one is moved by the other, we must needs find that if the first mover be taken away or cease to move, none of the others will move or be moved: because the first is the cause of movement in all the others. Now if an ordinate series of movers and things moved proceed to infinity, there will be no first mover, but all will be intermediate movers as it were. Therefore it will be impossible for any of them to be moved: and thus nothing in the world will be moved.vi

15 The third argument[15] amounts to the same, except that it proceeds in the reverse order, namely by beginning from above: and it is as follows. That which moves instrumentally, cannot move unless there be something that moves principally. But if we proceed to infinity in movers and things moved, they will all be like instrumental movers, because they will be alleged to be moved movers, and there will be nothing by way of principal mover. Therefore nothing will be moved.vii

16 We have thus clearly proved both statements which were supposed in the first process of demonstration whereby Aristotle proved the existence of a first immovable mover.viii


iIt is utterly absolutely painfully crucial that you understand what is meant by this. Aquinas means here-and-now, or at-this-very-moment causation. The stick moves the stone here-and-now, your arm moves the stick here-and-now at-this-very-moment, your muscles move your arm here-and-now at-this-very-moment, simultaneously. Your muscle and other cells here-and-now at-this-very-moment move, and so on down to something. Some first unmoved mover. It is this here-and-now at-this-very-moment chain which cannot proceed here-and-now at-this-very-moment to infinity. Update See YOS’s clarification on “instantaneous” movement/change below.

Ed Feser (who not uncoincidentally, since I’ve stolen many of my ideas from him, today wrote on a similar subject) has taken great pains in his many books and articles to teach that this per se chain of here-and-now at-this-very-moment causes exists here-and-now at-this-very-moment, that everything is happening at once. His experience has been that this teaching does not stick. Why? Who knows. But since it is so, I remind you we are not talking about accidental chains of causation, such as when one rock falls off a hill into another, and the second rock then hits a third, and so on. No no no no. We are talking about how movement or change in the here-and-now comes about. Meditate on the example until it is clear in your mind before continuing.

Or watch Feser’s terrific lecture on the subject.

iiAll of Aristotle’s Chapter 6 may be found here. The stick is a body, and so is your arm, and so are your cells, the chemicals, the electrons and neutrons, the quarks, the strings (if they exist) and whatever, if anything, is “below” them. Notice that Aquinas and Aristotle use a proof by contradiction. They assume there exists an infinite here-and-now chain.

iii Here-and-now at-this-very-moment!

ivSweet, no? If there did exist an infinite chain, and because we certainly see things move or change in finite time, this entire infinite chain would have to move not only in finite time, but at this moment, here and now (have we memorized this yet?). The proof immediately follows.

vAristotle proves even more than his: his book 7 may be found here. Anyway, it is clear that if we have an infinite here-and-now chain of objects, the whole thing must itself, here-and-now at-this-moment, move. And that is not possible in finite time. Worse, this would have to be the case for everything everywhere that is in the process of being moved or changed. That’s a lot of chains and lots of infinite movements! Since it is absurd that these infinite chains can move in finite time, yet things are moved or changed in finite time, the chains must not be infinite.

viIf the here-and-now chain is finite—this is an assumption, arguendo—and the first element is removed, the later parts also cannot move, which is obvious. Now I don’t think people understand how big infinity really is. It is not just big, nor even BIG, but horrifically huge. An infinite chain would have more than a googol of elements, which is 10100; it would have more than a googoplex of elements, which is 10googol. If you were to keep doing that operation, namely taking 10 to the power of the last result, and continuing once a second for a whole day, you still would not have got close to infinity. You would still be infinitely far away. But the, to us humans anyway, unimaginably long chain would have only just got started! Just to use your arm to move a stick to push a stone.

An infinite chain is one which never stops. It goes on and on and on and always on some more. If infinite chains existed, there would not and could not be a first element. How, then, would the whole thing get started? Answer: it could not. It would be impossible—not unlikely, but impossible.

I think people believe infinity isn’t all that big because of mathematical analysis, and used in many areas of science. In analysis we regularly and somewhat glibly call on infinity. We say some function converges (perhaps) “O(n2)”, meaning as the number of elements grows, the finite function gets closer and closer to its infinite cousin. We plug in n = 20 or even n = 100 and see that the function is “settling down”, i.e. approaching some obvious value, and we think, “Ah, infinity and n = 100 aren’t that far apart.” However useful an approximation our function at some finite number of elements is, it is never the real value of the function at infinity. Taking approximations as reality and not just as approximations is a common, though not usually painful, fallacy.

It’s a killer here, though. When we are talking movement or change, we cannot have an approximation. We must needs have the whole chain. Stopping at the first (say) 100 elements just won’t do. If we remove a link, the chain cannot pull. And if we do have an infinite chain, there will be nothing to give the chain impetus. Without a first mover, nothing can happen. The chain thus cannot be infinite.

viiThe rock is being moved instrumentally by the stick, which is being moved instrumentally by the arm, and so forth. The principal unmoved mover sets off the whole shebang. I think we get it by now.

viiiLet’s review. We proved the premises in this First Way:

Whatever is in motion is moved by another: and it is clear to the sense that something, the sun for instance, is in motion. Therefore it is set in motion by something else moving it. Now that which moves it is itself either moved or not. If it be not moved, then the point is proved that we must needs postulate an immovable mover: and this we call God. If, however, it be moved, it is moved by another mover. Either, therefore, we must proceed to infinity, or we must come to an immovable mover. But it is not possible to proceed to infinity. Therefore it is necessary to postulate an immovable mover.

The premises being true, and the argument valid, the conclusion must also be true. And therefore it would irrational to deny it. But why God as the unmoved mover? Why not call the immovable mover the Higgs Field Driver or whatever? Well, we haven’t fleshed this part of the proof out yet, so our modern scientistic suspicion is natural.

As a hint—and only a hint—there cannot be more than one immovable mover, one unchangeable changer. There must be something which exists which acts to sustain everything. Stay tuned!

Next installment.

[10] 7 Phys., l.c.
[11] L.c.
[12] 7 Phys. i. ii.
[13] Ch. vii.
[14] 8 Phys. v.
[15] Ibid.

Summary Against Modern Thought: Potency, Actuality, & Movement

This may be proved in three ways. The first...

This may be proved in three ways. The first…

See the first post in this series for an explanation and guide of our tour of Summa Contra Gentiles.

Previous post.

Last time we only proved one premise, that some things move. Review this first or else you will be lost. This was an observational premise. Of course, some, sensing the coming inescapable conclusion to this argument, suggested with Parmenides that things don’t actually move or change because they only move “relatively”, or whatever. None of these counters are in the least convincing, as we’ll further see. Settle in, we have a lot to do today.

Chapter 13: Arguments in proof of God’s existence

4 This argument contains two propositions that need to be proved: namely that whatever is in motion is moved by another,i and that it is not possible to proceed to infinity in movers and things moved.ii

5 The first of these is proved by the Philosopher in three ways.iii First, thus. If a thing moves itself, it must needs have the principle of its movement in itself, else it would clearly be moved by another.iv Again it must be moved primarily, that is, it must be moved by reason of itself and not by reason of its part, as an animal is moved by the movement of its foot, for in the latter way not the whole but the part would be moved by itself, and one part by another. Again it must be divisible and have parts, since whatever is moved is divisible, as is proved in 6 Phys.[2]v

6 These things being supposed, he argues as follows. That which is stated to be moved by itself is moved primarily. Therefore if one of its parts is at rest, it follows that the whole is at rest. For if, while one part is at rest, another of its parts were in motion, the whole itself would not be moved primarily, but its part which is in motion while another is at rest. Now nothing that is at rest while another is at rest, is moved by itself: for that which is at rest as a result of another thing being at rest must needs be in motion as a result of the other’s motion, and hence it is not moved by itself. Hence that which was stated to be moved by itself, is not moved by itself. Therefore whatever is in motion must needs be moved by another.vi

7 Nor is this argument traversed by the statement that might be made, that supposing a thing moves itself, it is impossible for a part thereof to be at rest, or again by the statement that to be at rest or in motion does not belong to a part except accidentally, as Avicenna quibbles.[3] Because the force of the argument lies in this, that if a thing moves itself primarily and of itself, not by reason of its parts, it follows that its being moved does not depend on some thing; whereas with a divisible thing, being moved, like being, depends on its parts, so that it cannot move itself primarily and of itself.vii Therefore the truth of the conclusion drawn does not require that we suppose as an absolute truth that a part of that which moves itself is at rest, but that this conditional statement be true that if a part were at rest, the whole would be at rest. Which statement can be true even if the antecedent be false, even as this conditional proposition is true: If a man is an ass he is irrational.viii

8 Secondly,[4] he proves it by induction, thus. A thing is not moved by itself if it is moved accidentally, since its motion is occasioned by the motion of something else. Nor again if it is moved by force, as is manifest.ix Nor if it is moved by its nature like those things whose movement proceeds from themselves, such as animals, which clearly are moved by their souls.x Nor if it is moved by nature, as heavy and light things are, since these are moved by their generating cause and by that which removes the obstacle to their movement.xi Now whatsoever things are in motion are moved either per sexii or accidentally; and if per se, either by force or by nature: and if the latter, either by something in them, as in the case of animals, or not by something in them, as in the case of heavy and light bodies. Therefore whatever is in motion is moved by another.

9 Thirdly,[5] he proves his point thus. Nothing is at the same time in act and in potentiality in respect of the same thing. Now whatever is in motion, as such, is in potentiality, because motion is the act of that which is in potentiality, as such.[6] Whereas whatever moves, as such, is in act, for nothing acts except in so far as it is in act. Therefore nothing is both mover and moved in respect of the same movement. Hence nothing moves itself.xiii

10 We must observe, however, that Plato,[7] who asserted that every mover is moved, employed the term movement in a more general sense than Aristotle. For Aristotle took movement in its strict sense, for the act of a thing that is in potentiality as such, in which sense it applies only to divisible things and bodies, as is proved in 6 Phys.[8] Whereas according to Plato that which moves itself is not a body; for he took movement for any operation, so that to understand or to think is a kind of movement, to which manner of speaking Aristotle alludes in 3 De Anima.[9] In this sense, then, he said that the first mover moves itself, in as much as it understands, desires and loves itself. This, in a certain respect, is not in contradiction with the arguments of Aristotle; for it makes no difference whether with Plato we come to a first mover that moves itself, or with Aristotle to something first which is altogether immovable.xiv


iYou, dear reader, are potentially in Cleveland. Unless you’re not actually there, you are not actually there, but you potentially could be. Right? Now what could bring you there? Well, many things. A car, your feet, a plane. Unless you are dead, there is no logically necessary reason you couldn’t (sometime) be there. Point is this: if you are now here and later in Cleveland, some actual thing or things caused you to be there. It could not have been the potential of you being in Cleveland that caused you to be there.

In front of us is a blank canvas. It is potentially a painting of a horse. If it becomes such, some actual thing caused it to be. That it was potentially a picture of a horse could not be the cause. That is, the potential is not and cannot be a cause. Some actual thing or things was the cause.

A block of wood that is here may potentially be there, but to get there some actual thing must cause it to move. The potential that is there cannot be a cause. And so on.

We need these observations for background.

iiOnly the first premise today. This premise is handled later. As promised, slow going.

iiiWe only do this first proof today.

ivAn animal can move itself, as the next premise demonstrates. But pay attention to what it means when an animal moves itself. A rock, for instance, or a molecule of oxygen in the atmosphere must be moved by something actual.

vHere is Aristotle on this crucial subject (from Aquinas’s footnote):

Further, everything that changes must be divisible. For since every change is from something to something, and when a thing is at the goal of its change it is no longer changing, and when both it itself and all its parts are at the starting-point of its change it is not changing (for that which is in whole and in part in an unvarying condition is not in a state of change); it follows, therefore, that part of that which is changing must be at the starting-point and part at the goal: for as a whole it cannot be in both or in neither. (Here by ‘goal of change’ I mean that which comes first in the process of change: e.g. in a process of change from white the goal in question will be grey, not black: for it is not necessary that that that which is changing should be at either of the extremes.) It is evident, therefore, that everything that changes must be divisible.

Thus divisible also means extended in space. Even photons, which haven’t any mass, are extended waves. They are not particles of no, or absolutely zero, size.

viIn other words, in those creatures capable of self-locomotion parts of them are being moved by other parts, as when you walk. Do not forget we are interested in the parts which are moving themselves, and how and why they move. Re-read the example given in the previous post. This is absolutely necessary to understand. We are at stick-moving-the-stone example, where your arm is moved by muscles are moved by cells are moved by chemicals are moved by individual atoms are moved by electrons and protons are moved by quarks are moved by strings (or whatever) are moved, ultimately, by an unmoved (and unmovable) mover all now, at this instant.

viiWhat might “a thing moves itself primarily and of itself, not by reason of its parts” mean? If a thing could move itself not by its parts, but primarily, it would be like—and this is a weak and fictional analogy—a psychic remaining still and concentrating his mental “powers” so that his body flies through the air. But of course, that would still involve the movement many physical things (physical forces must come into play to interact with the body to shift it) and of the mental powers themselves, from a quiescent to active state, so it doesn’t ultimately work (see below). The point Aquinas is saying is that nothing can move primarily. Something must set off (and sustain) every motion or change. And, as above, this something must be something actual and not potential.

viiiZing! Ha ha ha! The great man himself with a hilarious pun.

ixThese are self-evident.

xThomas does not mean to invoke the psychic example, but by soul he means, if you like, by consciousness. Anyway, if the soul moves its object, then another has moved that object.

xiThat this premise is outdated doesn’t change the proof. A light thing is moved by (say) the wind, and not primarily; or it is moved accidentally or by a force, etc.

xiiPer se, i.e. by virtue of itself; accidentally, here by one part pushing another, or the whole being pushed by something exterior, as in you in a TSA groping line at the airport.

xiiiIf you are moving from A to B, it is only because you are potentially in or at B that you can move. If it is impossible—and not just unlikely, however unlikely—then you are not potentially in or at B. And since potentiality cannot be a cause, it must be act, or something actual, which is driving the movement. The key to this argument is “Therefore nothing is both mover and moved in respect of the same movement.” Understand that, and you have it made. All three parts are necessary: the mover, that which is moved, and this here and now movement.

xivIsn’t that pretty? Exciting, too, because our task is not only to prove God’s existence, but, having done so, to show what we can about God’s nature. This is a kind of first step in that direction. Here, don’t forget that Aristotle and Plato do not mean just physical movement from A to B, but change of any kind; Plato includes changes in, if you like, thinking, or willing; Aristotle does not. The psychic analogy might be welcomed by Plato but not Aristotle. Our intellects are not material, and therefore not divisible or extended.

Again, it is an act which must change something in A but which is potentially in B to B. It will turn out that God is, in Aristotle’s and Thomas’s terms, pure act or actuality itself, with no potentiality (this was not proved today). This is another reason to thoroughly grasp the difference between act and potential. We’ve only done a bare outline. For the terrific introduction in modern language, see Ed Feser’s new Scholastic Metaphysics: A Contemporary Introduction. Note: I’ll be reviewing this book soon.

All that was proved today was whatever is in motion is moved by another. Every scientist accepts this premise. In this sense, today’s arguments were scientific proof. This premise is something upon which all science relies. Its implications are, of course, deeper than science, but it encompasses the motivating force behind science. No scientist says, “This went/changed from A to B for no reason whatsoever.”

Don’t forget we have one more premise in the first way (of proof of God’s existence). Then we have a whole second way.

[2] [Physics] Ch. iv.

[3] 2 Suffic. i.

[4] 8 Phys. iv

[5] 8 Phys. v. 8.

[6] 3 Phys. i. 6.

[7] Phoedrus xxiv. (D.).

[8] L.c.

[9] Ch. vii.

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