Thursday, June 7, 2012
Oerter on motion and the First Mover
George Mason University physicist Robert Oerter has completed his series of critical posts on my book The Last Superstition. I responded to some of his remarks in some earlier posts of my own (here and here, with some further relevant comments here and here). In this post I want to reply to what he says in his most recent remarks about the Aristotelian argument from motion to an Unmoved Mover of the world.
All or some?
The version of the Scholastic principle of causality relevant to the argument from motion holds that any actualized potential must be actualized by something already actual. A common and more colloquial (but also potentially misleading) formulation would be: Whatever changes must be changed by something else. Now in one of his most recent posts, Oerter claims that, in the course of defending the argument from motion in The Last Superstition:
Feser abandoned [this principle], and replaced it with something like “Some things that changed [sic] are changed by something else.” This is fatal to his argument, though…
[Feser’s argument] obviously relies on the idea that everything that changes is being changed by something external to it. If only some things that change require an external changer, then the argument is just a non sequitur.
Now this is quite bizarre. Oerter is correct when he says that to abandon the principle of causality and replace it with a weaker premise like “Some things that change are changed by something else” would undermine the argument. But in fact I never abandoned the principle and never adopted the weaker alternative principle Oerter attributes to me. Why does he claim otherwise?
The reason is that Oerter has badly misinterpreted the remarks about Newton’s principle of inertia that I made in the book. What I said was that even if we allow (at least for the sake of argument) that Newton’s law accounts for local motion (i.e. change of place) of a uniform rectilinear sort, there are still other kinds of change that it would not account for. Oerter reads this as an affirmation that inertial motion does not have a cause even if other kinds of change do. But I never said, and would never say, that such motion does not have a cause. What I said is that even if we allowed that such motion is in some respects “explained” by Newton’s law, (a) there are other kinds of change that the law would not explain, and (b) Newton’s law would not be a complete explanation even of local motion, both because it does not explain the acquisition or loss of momentum, and because the operation of the law itself stands in need of explanation. And none of that entails that uniform rectilinear local motion does not have a cause.
What is the cause of such motion? To take a concrete example, what is the cause of the inertial local motion of a stone which someone has thrown into the air? Well, here’s an answer some Aristotelians would favor. First of all, on one Aristotelian interpretation of laws of nature, a law is shorthand for a description of the way a thing will operate given its nature or substantial form. And in the case of inanimate natural phenomena, the efficient cause of their natural operations is whatever generated them and thus gave them their substantial forms. So, part of the cause of the stone’s inertial motion is whatever natural process brought the stone into existence and thereby imparted to it a substantial form of the sort that entails operation according to the law of inertia. But that is only a necessary condition of the stone’s inertial motion, since something needs to set it in motion in the first place. And of course, what set it in motion is whoever threw it into the air. Hence (on the Aristotelian account in question) the total efficient cause of the current inertial local motion of the stone in question would be the thrower of the stone together with whatever natural processes generated the stone.
Now other Aristotelians have put forward different analyses; and as I have said before, I discuss these issues in greater depth in my article “The medieval principle of motion and the modern principle of inertia,” forthcoming in the Proceedings of the Society for Medieval Logic and Metaphysics. The point for present purposes is merely to note that there is nothing in Newton’s law that entails that inertial local motion lacks a cause. And I certainly never claimed that it lacks a cause!
“First” in what sense?
Scholastic writers distinguish between accidentally ordered and essentially ordered causal series. A stock illustration of the former kind of series is a father who begets a son who in turn begets another. A stock illustration of the latter sort of series is a hand which uses a stick to move a stone. The stick in the latter example has no power on its own to push the stone; it moves the stone only insofar as it is being used by the hand as an instrument for moving it. By contrast, a man who begets a son does have the power to do so inherently, “built in” as it were. It really is he who begets his son; it is not his own father who does so, using him as an instrument. (These are, though, merely illustrations intended to jog the ideas in question, and as I explained in a recent post, nothing rides on the precise empirical details.)
Now it is essentially ordered series rather than accidentally ordered series that necessarily have a first member. But “first” here doesn’t mean “the member that comes at the head of the line, before the second, third, fourth, etc.” Rather, “first” means “fundamental” or “underived.” The idea is that a series of instrumental causes – causes that have their causal power only derivatively, only insofar as they act as instruments of something else – must necessarily trace to something that has its causal power in a non-instrumental way, something which can cause without having to be made to cause by something else. And the argument from motion claims that only that which is pure actuality -- that which is, as it were, “already” fully actual and thus need not (indeed cannot) have been actualized by anything else -- can be causally fundamental or underived in an absolute sense.
This does not require such a cause to come at the head of some metaphysical queue. Even if we suppose there to exist a series of instrumental causes that regresses to infinity or loops around in a circle, there would still have to be a “first” cause in the sense of an underived or non-instrumental cause outside the infinite regress or loop, otherwise the infinite or circular series as a whole -- comprised as it is of instrumental causes having no causal power of their own -- could not exist. As some Thomists have put it, a paintbrush has no power to move itself, and it would remain powerless to move itself even if it had an infinitely long handle. (I have addressed this issue in an earlier post and in my book Aquinas. I have also explained in another post that Aquinas does not in fact think that God causes the existence of things through intermediate causes -- talk of such intermediate causes is best read in a “for the sake of argument” way.)
This brings us to another respect in which Oerter’s comments about the argument from motion come to grief. About essentially ordered causal series, Oerter says:
[T]he idea that causes can be arranged in nice ordered chains as envisioned by Feser just doesn't accord with what we know about the way the universe works…
Think about two masses, A and B, in circular orbits around their common center of mass…
The change in A's velocity is caused by B's gravity, and the change of B's velocity is caused by A's gravity. There's no need for one of these to be causally prior to the other.
Instead of nice ordered chains of causality, there are complex interconnecting webs of interactions. When all the causes are present at once, as they are in the situations Feser calls "essentially ordered chains," no one of them need be considered the "first."
The trouble with this is that it assumes that the Scholastic is arguing for a “first mover” in the sense of a mover coming at the head of a line. And as I have just explained, that is not what is at issue. Let a system of causes be as complex as you wish -- an infinite series, a circle, a vast crisscrossing network -- to the extent that they are instrumental in character, there will have to be something outside the system as a whole imparting causality to it.
Oerter raises a more interesting objection when he writes:
[E]verything in the world has the "power of movement in itself"… Changes, for the physicist, are the result of forces, and forces are part of the nature of those fundamental particles from which everything is made. It is the nature of massive particles to exert the gravitational force, of charged particles to exert the electromagnetic force, and so on. So any particle (or collection of particles) can be the "first mover" in the series.
What Oerter doesn’t realize, though, is that (apart from a qualification here or there), this isn’t a criticism of the Aristotelian-Scholastic position; on the contrary, it just is the Aristotelian-Scholastic position! The notion that material substances operate in the regular ways uncovered by physical science by nature, by virtue of something inherent to them, is the core of the Aristotelian-Scholastic doctrine of substantial form -- the doctrine that the early moderns reacted against and replaced with the notion of matter as something inherently passive. (As some contemporary philosophers of science and metaphysicians with no Thomistic or theological ax to grind have emphasized -- see the work of Nancy Cartwright, Brian Ellis, and other writers of a broadly “new essentialist” or "dispositional essentialist" sort -- modern science is in fact better interpreted in neo-Aristotelian terms rather than in terms derived from modern post-Cartesian and post-Humean philosophy. I developed this point at the end of The Last Superstition, which makes it odd that Oerter overlooks it.)
Indeed, for the Aristotelian-Scholastic tradition, living things just are “self-movers” in a loose sense: Unlike a stone (say), a dog, bird, or snake can in an obvious sense move itself toward the realization of the ends toward which its nature points it (food, mating opportunities, etc.). And while inorganic natural substances don’t move themselves in the same manner, their behavior is nevertheless “spontaneous” in a way the operations of artifacts are not. (I borrow the term from James A. Weisheipl’s Nature and Motion in the Middle Ages, essential reading on the issues under discussion.) What that means is, not that their activity is without a cause, but rather that it flows from something immanent or intrinsic to them, from their very nature rather than being imposed from outside. There is nothing intrinsic to a watch that makes it tell time; that end is imposed on the metal parts by a designer. But there is, just as Oerter says, something intrinsic to particles by virtue of which they exert gravitational or electromagnetic force. Now the cause of their doing so is whatever generated them and (thereby) gave them their substantial forms. Once they exist, though, that activity just follows from their nature. (This is one reason why Thomists are frequently critical of “Intelligent Design” theory. To model natural substances on artifacts is precisely to misunderstand them. See my post on the Aristotelian distinction between “nature” and “art,” and my other posts on the dispute between Aristotelian-Thomistic philosophy and ID.)
All the same, natural substances are not the source of their activity in an absolute and ultimate sense. For any material substance is a composite of substantial form and prime matter; and since prime matter exists only as actualized by substantial form, while substantial form is a mere abstraction unless instantiated in prime matter, we will have an explanatory vicious circle unless we appeal to something outside the form/matter composite which sustains it in being. And this can, ultimately, only be that which is purely actual (and thus something for which the same vicious circle cannot arise). Furthermore, any material substance is a composite of an essence together with an act of existence, and thus in need of something which combines these metaphysical parts if it is to persist in being at any particular instant. And this can, ultimately, only be something whose essence just is existence, that which is subsistent being itself (and thus something which need not and indeed could not have a cause which combines its essence with a separate act of existence). I develop these themes at length in my American Catholic Philosophical Quarterly article “Existential Inertia and the Five Ways” (which can be read online by Googling the title, scrolling down to the fourth or fifth result, and clicking on “Quick view”).
In a further post on the subject of motion, Oerter (after mistakenly implying yet again that I have “abandoned” the claim that whatever changes is changed by something else) says that in an earlier response to him I had “claim[ed] that inertial motion is not real change,“ though Oerter also suggests that I am “cagey” about whether this is really what I think. He then goes on to characterize this view as “a perfect example of the kind of absurdity you get when you don't allow physics to inform your metaphysics.”
But I did not assert that “inertial motion is not real change,” cagily or otherwise. What I said is that inertial motion is often characterized as a “state” -- by physicists themselves, mind you (which makes it rather odd for Oerter to accuse me of not “allowing physics to inform metaphysics,” but never mind). And I noted that if inertial motion is a state (and thus not a real change), then there could not be even a prima facie conflict between Newton’s law and the principle of causality. But I did not claim that this is in fact the correct way to characterize inertial motion. On the contrary, in the post to which Oerter is responding I also wrote that:
Newton’s law is descriptive. It tells us how a body behaves, but not why it behaves that way. Thus the law does not rule out the thesis that the reason a body so behaves is because of a “mover” which actualizes its potencies for motion. (To be sure, the law does rule out any scenario where a body continues at rest or uniform rectilinear motion while acted upon by physical forces impressed upon it. But -- to appeal once again to the analogy with Kepler’s laws -- the principle of causality no more requires that what actualizes a potency is, specifically, a physical force of this sort than to affirm a cause of the orbits of the planets requires positing a special kind of massive body additional to the sun, planets, asteroids, etc.)
In other words, I explicitly considered the alternative interpretation of inertial motion on which it involves genuine change, and pointed out that even on that interpretation Newton’s law is not incompatible with the principle of causality. Now it is true that in the immediate surrounding context of this particular passage I also say that Newton’s law and the principle of causality are not using “motion” in precisely the same sense. And perhaps that led Oerter mistakenly to conclude that I was asserting that Newton’s law is not describing genuine change. But my point was that the principle of causality is talking about any actualization of potential, while Newton’s law (a) is talking only about local motion specifically and (b) by itself says nothing one way or the other about whether local motion involves the actualization of potential. And that leaves open the question of whether inertial motion does involve real change.
Now the reason I did not assert one way or the other whether inertial motion involves real change is that that particular question simply needn’t be settled in order to defend the argument from motion against the charge that it somehow conflicts with Newton’s law. On either interpretation, the principle of causality is perfectly compatible with Newton’s law. Indeed, part of my point -- though in fairness to Oerter, this is a point I develop in my book Aquinas (which he has not read) rather than in The Last Superstition -- is that the objection from Newton’s law is not even well-defined in the first place. It rests on ambiguities any resolution of which leaves the objection without force. In fact, the burden of proof isn’t on the Thomist to show that his argument is compatible with Newton’s law; the burden is on the critic to show that it is not compatible.
In particular, to show that there is any conflict, the critic has to explain exactly what it means to characterize inertial motion as a “state”; exactly how inertial motion can amount to real change if it really is a “state”; exactly how Newton’s law could conflict with the principle of causality even in principle if inertial motion does not involve real change; exactly how Newton’s law is incompatible with the principle of causality (and not merely with the influence of physical forces) even if inertial motion does involve real change; exactly what it means to characterize Newton’s principle as a “law” and exactly how the notion of a “law” can be cashed out in a way that doesn’t entail a tacit commitment to the very Aristotelian conception of nature (including substantial forms, etc.) that the argument from motion rests on; and so forth. And as I argue in Aquinas (and at greater length in the forthcoming article) critics of the principle of causality who appeal to Newton have not done this. The standard procedure is just glibly to assert that there is a conflict, without bothering to address any of the issues that would have to be worked out before a claim of conflict could be justified.
And Oerter adds nothing substantial to the critic’s case. Instead, he tells us that a better account of motion would, among other things, “declare that velocity doesn't need an explanation (it is something that is just in the nature of massive objects).” This is quite rich coming from a critic of the Aristotelian-Thomistic position -- A-T writers are, after all, constantly accused (falsely) of trading in pseudo-explanations of the “it’s just in the nature of…” sort! Of course, no Aristotelian or Thomist would begrudge Oerter an appeal to the “nature” of a thing. The difference between Oerter and us A-T types, though, is that we would never leave it at that. We realize (as Oerter seems not to) that we still need an account of what a nature is and why a thing has the nature it does in the first place. And those questions lead, for the reasons alluded to above, precisely to the conclusion Oerter wants to avoid -- to the existence of a purely actual cause of a thing’s persistence in being, with the nature (i.e. substantial form) it has, at any given moment.
A purely actual first mover?
In the last few paragraphs of the post in question, Oerter seems to allow that if we are speaking of motion or change in the Aristotelian sense of the actualization of potentials and are thinking in terms of essentially ordered causal series, then we do indeed get to a first mover. But he claims that this does not yet get us to a purely actual mover.
But what Oerter fails to see is that any mover that is less than purely actual will, by virtue of being composite (composed of form and matter, or essence and existence) require an actualizing cause outside it, which means that no such mover can truly end the regress of actualizers. Only what is purely actual could do that even in principle. Again, I elaborate on all this in “Existential Inertia and the Five Ways” -- which (I emphasize for those who would object to having to buy and read one of my books) is an article rather than a book, and available online.