Two bases for “everything in motion is moved by another”

Aristotle in his Physics and St. Thomas in his First Way both claim that anything in motion is moved by another, though they give differing but complementary accounts of why it is true.

For St. Thomas, the premise follows from the fact that “what is in motion”, when taken strictly, is potential. The thing that moves from A to Z can’t be by nature A or Z, but has to have both as possibilities. The “other” that moves this thing is primarily the “Z” that serves as the terminus of the motion, and secondarily whatever it is that has the power to push the thing to Z. The argumentation here is extraordinarily tight: all it requires is the minimal claim that motion means to move from one thing to another, and that what undergoes this is neither necessarily the one thing or the other.

Aristotle appeals to a different grounding premise. For him, “what is in motion” is necessarily a whole extended body, and each part of the extension is other than the body. All of this rests on the interesting claim that it is impossible for a non-extended body (a Euclidean point) to change in any way, even to change place. One can imagine say, this dot


moving across the screen, but Aristotle would claim that it cannot move. What exactly it can do is unclear, and there are several logical possibilities: either we are not imagining a point doing anything, or whatever the point was doing could not be considered motion, or any possible motion could not be a physical process (a mathematical one, perhaps?) etc. But at any rate the point can’t move: since in order for anything to move it has to move to the next place, but a point could only be here and then be there, it couldn’t move from one thing to another.

Here again, we encounter the minimal claim that motion means moving from one thing to another, but it is taken as meaning that what moves is an extended whole that requires “others” to move, namely, its parts.

Notice that on the Thomistic account, the mobile is considered as incomplete; on Aristotle’s account the mobile is considered as whole and complete but dependent on its parts. The Thomistic account gives us a mobile that is an open system receiving energy and intentional direction from the outside, Aristotle’s account is of a closed system that has an activity in virtue of its parts. I use closed and open in a broader sense than they are used nowadays – for example, a falling stone, considered as just the stone, is a closed system in the sense we are using here, though it includes the complex moving closed systems of modern physics too.

And so the differing accounts of “everything in motion is moved by another” give us a metaphysical foundation for our ability to consider nature as both an open and closed system. The differing accounts lead us to different accounts of the first source of motion as well. For Aristotle, the first source is partless and non-physical; for St. Thomas it is purely actual and in conscious possession (as opposed to physical possession) of the terms defining the motion.


  1. mhumpher said,

    January 2, 2014 at 11:42 am

    Could you imagine a point at all? Everything we image has some extension and not even our imagining of lines, for example, are actual mathematical line but have color, imperfections and width.

  2. PatrickH said,

    January 2, 2014 at 12:51 pm

    I don’t understand why “omne autem quod movetur ab alio movetur” is translated as “everything in motion is moved by another”. “movetur” is unambiguously in the passive voice, i.e., “is moved” or “is being moved”, and is contrary to “in motion” precisely since (to an English reader) “in motion” has the connotation of meaning “is moving”, i.e., the active voice, in the intransitive sense. It strikes me as perverse to translate two instances of the very same word in the very same sentence in two ways, one as an implied intransitive active, and the other as overtly passive transitive.

    If St Thomas is saying “everything that is being moved is being moved by some other” he is precisely evoking the impossibility of the passive recipient of the transitive motion being identical with the active giver of that transitive motion. “X is moved by Y to Z” means the same thing as “Y is moving X to Z”, which means that Z cannot possibly be the other that is actively transitively moving X.

    He says in the very next sentence “nihil enim movetur nisi secundum in potentia ad illud ad quod movetur”(I missed a word or two in there) and again is translated as “for nothing is in motion except insofar as it is in potency to that to which it is being moved”, which again ignores what strikes me as the plain meaning of the sentence, which is that nothing is being moved except insofar as it in potency to that to which it is being moved, in other words nothing is (in the process of) being moved except insofar as it’s not at its destination yet.

    Identifying the “other” with the “illud” strikes me as perverse. It is being moved by some other than itself to some end-state, not being moved by and to the very same thing. After all, in the sentence after that, something moves (actively, transitively) only insofar as it is in act. How can the end-state, which is in potency be in act at the same time? The end-state of a motion is not the mover in the mover-moved transitive relationship which exists in perfect correlative simultaneity in the present moment, since they are simply two sides of the same singular transitive relationship.

    Unless I am missing some subtlety of the translation, of course.

    • January 2, 2014 at 7:25 pm

      Latin, as you know, has only one aspect in the present tense, and so it can’t distinguish between the imperfect, perfect, or simple, and beyond this its simple is (like English) unable to distinguish actions from states of being. Disco can both mean “I’m teaching (right now)” or “I teach” (as a description of what I do). The same applies to the passive voice (I’m educated, I’m being educated). I’m following the contemporary tradition by taking the first “movetur” as indicating a state, and the use of the prepositional phrase helps to make this clear.

      Identifying the “other” with the “illud” strikes me as perverse. It is being moved by some other than itself to some end-state, not being moved by and to the very same thing.

      The end is the cause of the agency of the agent, and so I stand by my description. The agent is first only in the way that matter or potency is. Again, the first sense of “act” is the terminus of the change, and this end is first in the causal order, even if not in time. That said, the post makes reference to the causality of the agent as well.

      • PatrickH said,

        January 3, 2014 at 9:22 am

        My own translation of movetur as “is being moved” was partly inspired by your own mention of the possibility of translating it in the progressive sense (being moved). Unfortunately, I can’t remember the post where you said that. In any case, I’m still not certain that the state-like sense you refer to as being that of the first “movetur” is not better translated as “is moved” rather than “is in motion”. Alfred Freddoso, for example, translates the sentence as: “But everything that is moved is moved by another.”

        Now anything that is moved is always moved by something (that’s inherent in the passive voice), and even the state-like sense “it is moved” still indicates that what-is-moved acquired that state passively. STA does seem to be arguing here that anything that is moved is always moved by something, but that something can never be the same as what is moved. Nothing can give to itself what it does not have, and can only receive what it does not have, so the same thing cannot give and receive in the same respect at the same time.

        In any case, instead of wasting your time with translation arguments, I’d rather waste your time indicating the source of my confusion. STA provides as illustrative examples in the First Way 1) the piece of wood becoming hot and 2) the hand moving the stick. Now the examples clearly refer to a piece of (cold) wood being placed (by hand) onto a burning wood fire, becoming hot (i.e. hot enough to get on fire itself), so hot that to move it you can’t use your hand directly but have to grasp a stick and poke at it.

      • PatrickH said,

        January 3, 2014 at 9:24 am

        This is the second part of my comment. Sorry about the length, but I am confused here.

        When applying this example, it seems that STA is saying the actual heat of the fire (or the wood in the fire, with the fire being its heat) “moves and alters” the piece of wood from being potentially hot to being actually hot. It doesn’t seem to me that it makes sense to say that STA is referring to the heat the piece of wood attains at the end of the heating-up process as what “moves and alters” it when it’s still in the process of getting hot. Isn’t it the “fire” whose actual heat moves and alters the potentially (not-yet) hot wood, the heat the wood receives in order to get hot itself, isn’t that the heat of the wood fire when the wood is placed upon it? Isn’t that the mover, the giver, what is “in act”, what “leads out [the wood being hot] from potency into act”?

        Please forgive my questioning tone. I certainly do not intend to sound disagreeable, though I fear I have. My problem is that I have had a great deal of difficulty understanding the First Way, and it seems to me I only made progress when I used the examples provided by STA to help me understand what he means by “mover”, “moved” and “moving”, as well as “in act” and “in potency”, to say nothing of all those “quods”, “aliquods”, “aliquids” and that darned “illud”.

        Sigh. I fear I will never understand any of the other of the Five Ways if I do not get a clearer grasp of this one. The First Way is the “manifestior” (more obvious, unmistakable, flagrantly evident) way, the one built on what “sensu constat” (what the senses confirm in the strongest possible way), and yet it is clearly not the argument itself that is umistakably obvious nor testified to by the senses (it’s damnably tricky, if you ask me), but rather it proceeds from the unavoidable phenomenal in-your-face reality experienced by his readers hundreds or thousands of times in their lives (“in hoc mundo”): the unmistakable difference between a piece of wood cold enough to pick up in your hand and that same piece of wood a short time later that has become so hot you have to use a poker to move it.
        In other words, the First Way is “A piece of not-hot wood becomes a piece of hot-wood…therefore God exists.” It’s all that in-between argumentation, the “…” that’s messing with my mind.

      • PatrickH said,

        January 4, 2014 at 7:41 am

        Ah, at last the ice-cold lump of wood that is my brain is heated by the fire of the First Way. Of course you are right. I fell into the trap of thinking that change is best understood as a tracking over time of something changing by being pushed along some path through a succession of moments until it stops getting pushed. That’s wrong (or incomplete) because it doesn’t take into account precisely the role of the terminus as itself in act and therefore a mover.

        Sorry about my incomprehension. All I can say is that my respect for STA, already high, is now immense. I found your discussion very helpful in the end, as well as that of Joe Sachs in his article on Aristotle’s theory of motion.

  3. K.L.Anderson said,

    January 2, 2014 at 1:23 pm

    I see the cosmos something like the way Frederick Turner sees time, “cause and effect is not a chain but a branching tree in both temporal directions.” The same cause can have many different effects and the same effect can result from many different causes.

    I avoid the metaphysical and theological hairsplitting about “first causes” by not seeing a first cause. I see an endless branching of cause and effect.

    This worldview harmonizes with the belief that we evolve to Godhood materially and supermaterially, a Godhood which is not the first cause.

    There are always cosmos arising from a Primal Material and the activating supermaterial Spirit-Will within the primal material, never separate from it.

    Religion, Godhood and even science can survive and prosper without a first cause.

    • January 2, 2014 at 6:05 pm

      Religion, Godhood and even science can survive and prosper without a first cause.

      I’ll pass over the Godhead claim, since I view divinity as uncaused anyway, and “religion” is no longer a coherent concept and so whether it remains or not is not a matter of systematic rigor or even truth. That leaves us with just science, and on this we disagree. Such a loss would severely damage science and even any systematic inquiry (like, say, detective work or journalism). It would mean we would have to have told people to stop looking for a malaria parasite, or ATP/P2X7R as the cause of diabetes, or Nixon as the cause of the Watergate cover up… We’d see it as pointless to distinguish a hitman from a contractor, a menial laborer from an architect, the designer from the factory assembly worker, etc. We’d be fine with Medieval ideas of fire as the cause of all heat and air as the cause of floating. We’d even be really confused by the plots of action, spy, or conspiracy movies, since we’d just sit there wondering “why all this bother over finding who is behind it all?” More to the point, the first cause is simply what the thing is, or the thing itself. Renouncing this is to give up even your “branching tree in both temporal directions.”

      But I suppose you see this as all merely relative, and the cosmic tree as the reality. But this still leaves first causes of motion, generation, transcendentals, etc. All of St. Thomas’s proofs remain.

      • K.L.Anderson said,

        January 2, 2014 at 7:13 pm

        You demonstrate the problem with so much theology, much cleverness, little real substance. We don’t stop looking for all causes because there is no first cause.

  4. Ashmen Dasgupta said,

    January 3, 2014 at 9:02 pm

    How would the first way be affected and subsequently the propostition that everything is moved by another if things could both be in potency and act at the same time and in the same way say to be actually hot and potentially hot. I was reading an interesting and subtle paper by Mark Sentesy called The Compatibility of Potency and Actuality which argues just along these lines that to make potency and act incompatible is incoherent.

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