The Scholastic principle of causality states that any potential, if actualized, must be actualized by something already actual. (It is also sometimes formulated as the thesis that whatever is moved is moved by another or whatever is changed is changed by another. But the more technical way of stating it is less potentially misleading for readers unacquainted with Scholastic thinking, who are bound to read things into terms like “motion” or “change” that Scholastic writers do not intend.)
In an earlier post I responded to an objection to the principle raised by physicist Robert Oerter, who has, at his blog, been writing up a series of critical posts on my book The Last Superstition. Oerter has now posted two further installments in his series, which develop and defend his criticism of the principle of causality. Let’s take a look.
Quantum mechanics and causality
Recall that in an earlier post Oerter claimed that quantum mechanics casts doubt on the principle of causality insofar as it describes “systems that change from one state to another without any apparent physical ‘trigger.’” Recall also that I pointed out that it is simply a fallacy to infer from the premise that QM describes such-and-such a state without describing its cause to the conclusion that QM shows that such-and-such a state has no cause.
In the first of the two further installments he’s posted since my response, Oerter replies to this sort of objection as follows:
This is a valid point. Just because quantum mechanics… is the most amazingly well-tested, most accurate, most far-reaching description of the universe that we have ever produced, we can't just conclude that it's the end of the story. Maybe quantum mechanics is incomplete - maybe there is some further, more precise, theory that will tell us about the causes of electron transitions and radioactive decay…
This very point was raised in a famous paper by Einstein, Podolsky, and Rosen, who argued in 1935 that quantum mechanics must be incomplete… An [sic] major advance came in 1964, when John Bell showed that (under a very general set of assumptions) any attempt to “complete” quantum mechanics would end up making predictions that differed from those of QM. This led to a series of experiments designed to look for such differences. The upshot: quantum mechanics has come out the winner in every test to date…
[A]ny additional “causes” added to quantum mechanics will result in violations of quantum mechanical predictions.
Let's suppose that there is some physical property - something not included in the quantum mechanical description - that determines for each atom exactly when the electron will decay. Call it property A. Since property A is a physical property, it must have some physical effect. If it has some physical effect, then it must be possible to separate out systems with one value of property A from systems with some other value. That is, we can use property A as a filter…
Applying this filter, we separate out a subset from our original set of identically prepared atoms. This subset, having a physical difference from the original set, will have a measurably different set of physical properties… Thus, this subset will violate the rules of quantum mechanics.
Now, I put it to you that the 100-year history of successful predictions of quantum mechanics strongly suggests that there are no such additional physical properties…
End quote. Now, to see what is wrong with this, recall the analogy I drew in my previous post with Kepler’s laws of planetary motion. I noted that it would be fallacious to argue from the premise that Kepler’s laws describe the orbits of the planets without making reference to any cause of those orbits to the conclusion that Kepler’s laws show that the orbits of the planets have no cause. And it would remain fallacious whatever you think about Kepler’s laws and whether or not you think the orbits of the planets have a cause. For the point has nothing to do with the truth or falsity of either the premise or the conclusion. It has to do instead with the logical relationship between the premise and conclusion. The premise doesn’t entail the conclusion, and it doesn’t even make the conclusion more probable. It is evidentially irrelevant to the conclusion.
Hence, suppose someone who insisted that Kepler’s laws do show that the planetary orbits have no cause responded to criticism of this fallacious inference by saying: “That’s a valid point. Even though Kepler’s laws have had tremendous predictive success, they may not be the end of the story. Maybe some future theory will posit some heretofore unknown massive bodies additional to the ones we already know about (the sun, planets, asteroids, etc.), which make the planets orbit the sun in just the way they do. But the problem is that if there were such further bodies, they would influence the ones we do know about in such a way that their behavior would not match Kepler’s predictions. So the success of Kepler’s laws strongly suggests that there are no such additional bodies. So Kepler’s laws really do give us reason to doubt that the orbits of the planets have any cause.”
Such a response would, of course, completely miss the point. For the point has nothing at all to do with the empirical question of whether there exist some heretofore unknown bodies additional to the sun, planets, asteroids, etc. which exert a causal influence on the rest of the solar system. The point is much simpler (though also much deeper) than that sort of issue. It is not a point about the existence of causes of this or that particular kind,but a point about causality as such. And the point is that Kepler’s laws, which merely describe the behavior of the planets, tell you nothing one way or the other about why the planets behave that way. They are not even addressing that question. Hence they cannot answer that question. Nor (we might note for those who eschew metaphysics) can they tell you whether the question is a good question, whether it has any answer in the first place, etc. To the issue at hand, they are simply irrelevant.
Now the same thing is true of the relationship between QM and the principle of causality. To point out that it is fallacious to infer from the premise that QM describes such-and-such a state without describing its cause to the conclusion that QM shows that such-and-such a state has no cause, is not to say that for all we know there may be some heretofore undiscovered physical property which exerts an influence on the energy level of the electron (or whatever). The point is much simpler (though also much deeper) than that sort of issue. It is that QM, which merely describesthe behavior of a system, tells you nothing one way or the other about whythe system behaves that way. It also tells you nothing one way or the other about whether the question of why it behaves that way is a good question, whether it has any answer in the first place, etc. To the issue at hand, QM is simply irrelevant.
This naturally brings us to another objection to his position that Oerter considers in his recent post, to the effect that the principle of causality is “a metaphysical premise that can't be contradicted by any possible set of observations.” Oerter’s reply is that to insist, on metaphysical grounds, that the actualization of a potential must always have a cause is either to beg the question against him, or to rest one’s position on definitions of the key terms (“actuality,” “potentiality,” “change,” etc.) without giving any reason to think that the terms so defined really capture anything in the real world.
To see what is wrong with this response, consider once again the fallacious inference from the premise that Kepler’s laws describe the orbits of the planets without making reference to any cause of those orbits to the conclusion that Kepler’s laws show that the orbits of the planets have no cause. Suppose that when you pointed out the fallaciousness of this inference to someone who made it, he replied: “Your position either begs the question against me or rests on arbitrary definitions!” Obviously this too would simply miss the point, since the criticism of the inference in question was not: “The orbits of the planets do have a cause, here’s my theory about what that cause is, here are the technical terms my theory makes use of, etc.” The criticism was rather: “Whether or not the orbits of the planets really do have a cause, the inference you are making is fallacious, because Kepler’s laws by themselves aren’t even relevant to that particular question.” Similarly, the inference from the premise that QM describes such-and-such a state without describing its cause to the conclusion that QM shows that such-and-such a state has no cause is fallacious, and it remains fallacious whether or not the principle of causality is true, whether or not the definitions of its key terms have any application to reality, etc. Even if the Aristotelian position turned out to be false, quantum mechanicswouldn’t be what falsifies it.
Oerter also addresses another potential objection to his position, to the effect that “the laws of quantum mechanics are the cause of the change [i.e. the change described in examples of the sort Oerter appeals to].” The first part of Oerter’s response is as follows:
This objection can be dismissed easily. The question is what causes the change to happen at the particular time it happens. QM is silent on this question.
Further, in most philosophical views of physical laws, the laws have no causal efficacy. For instance, we might think of laws as just descriptions of the way things actually behave. But a description of how something happens is not a cause of it happening. So, the moon's orbit around the earth isn't caused by the law of gravity. It's caused by the actual gravity of the actual earth.
Now as it happens I more or less agree with what Oerter says here. Indeed, it is ironic that he should say it, because it actually supports my position rather than his. Oerter writes that “we might think of laws as just descriptions of the way things actually behave.” Exactly. Laws -- including the laws enshrined in QM -- are descriptive. They tell you what happens, but they do not tell you why it happens that way. They may, of course, make reference to particular sorts of causal factors -- gravitation, mass, charge, etc. -- but the explication of these factors itself simply amounts to a further description of whatthese causes do, not why they do it. Indeed, the causality as such of gravitation, mass, etc. is, strictly speaking, irrelevant to the laws. That A and B will behave in such-and-such a way is all the law qua law commits you to; that A is the cause of B drops out as irrelevant. That is why Newton’s law of universal gravitation was so useful even when we had no clear idea of what gravity was or how it worked. And that is why positivists could hold that causality was a pre-scientific holdover which could be dispensed with. They were wrongto hold this, but the point is that they could hold it with a straight face in the first place only because the status of causality as such -- its nature and even its existence -- is something about which the laws of physics themselves (including the laws of QM) are silent.
But the status of causality as such is precisely what the principle of causality is about. And that is why QM has nothing to tell us about the principle of causality. They are simply not addressing the same question. Given that you have already determined on independentgrounds whether or not the principle of causality is true, QM may raise questions about how it is to be understood in contexts like that of the hydrogen atom (to allude to Oerter’s example). But there is nothing special about QM in that regard. One billiard ball knocking into another, melting and freezing, electromagnetism, gravitational attraction, plant and animal growth, volitional behavior, divine creation, all involve very different sorts of efficient causality. There are also distinctions to be drawn between essentially ordered and accidentally ordered causes, between causes that contain what is in their effects formally and those that contain what is in their effects only virtually, between total causes and partial causes, between the causality of substances and that of accidents, and so forth. If you think that all efficient causality reduces to some crude, deterministic billiard-ball model, then QM might seem to be a challenge to the very notion of causality. (“Look, there’s no little billiard ball deterministically pushing the electron into a higher energy level! Causality itself crumbles!”) But no Aristotelian or Scholastic would buy this simplistic conception of efficient causality in the first place. (Naturalist critics of Aristotelian-Scholastic arguments rarely beg one question at a time. They beg whole books full of questions.)
The principle of causality itself does not make any claim about how exactly efficient causes operate in all of these diverse cases. It just tells us that whatever the details turn out to be, any potential will only be actualized by something already actual. How does this work out in the case of QM? This brings us to the second part of Oerter’s response to the claim that the laws of QM are the cause of change. He writes:
Finally, even if we think of physical laws as having some sort of actual existence and causal efficacy, well, the laws of QM exist right at the moment the electron is excited, so by this view the electron should immediately decay. In Aristotelian terms, we are looking for the efficient cause: the thing that brings about the change at the instant it occurs. The laws of physics apply equally to all times; they can't be the reason something happens at some particular time.
(It seems to me that the laws of physics could be considered the formal cause in Aristotelian language. But Feser says that modern philosophers have abandoned formal (as well as final) causes. Does anyone know if laws can, or cannot, be considered formal causes?)
The answer to this latter question is: No, laws are not formal causes. Nor do laws have any sort of independent existence or efficacy as efficient causes. The correct thing to say from an Aristotelian point of view is rather something like this: Natural substances have essences or substantial forms that ground their characteristic patterns of operation. For instance, it is in virtue of the substantial form of a tree that it tends to sink roots and grow branches; it is in virtue of the substantial form of water that it tends to freeze at one temperature and boil at another temperature; it is in virtue of something common to the substantial forms of material objects in general that they exert a gravitational pull on each other; and so forth. Now a “law of nature” is a description of these patterns, a description of how things will tend to operate given their natures, essences, or substantial forms. The existence and operation of laws of nature thus presupposes the existence and operation of concrete natural substances. Indeed, strictly speaking it is not the laws that exist and operate; “laws” are mere abstractions from the concrete substances. What exist and operate are the concrete substances themselves. The laws are not even formal causes but rather mere descriptions of how things operate given their formal causes, i.e. their substantial forms. (See chapter 6 of David Oderberg’s Real Essentialism for an important recent treatment of laws of nature from an Aristotelian-Thomistic point of view.)
[This is, by the way, why “laws of nature” don’t really explain anything, at least not ultimately. The very idea is a holdover from a time when Descartes, Newton, and Co. wanted to chuck out the Aristotelian framework, and replaced the idea that things operate according to intrinsic natures or substantial forms with the idea of operation according to externally imposed divine commands or “laws.” Stripped of this theological context, the notion of a “law” must either be cashed out in Aristotelian terms of the kind suggested above, or in other metaphysical terms equally unwelcome to the naturalist, or -- as Nancy Cartwright has pointed out -- collapse into incoherence. It is ironic that atheists so unreflectively help themselves to an inherently theological idea, albeit an idea derived from modernist rather than Scholastic theology.]
In the case of the hydrogen atom (once again to appeal to Oerter’s example), what we have is a concrete system that behaves in the way described by QM. Now as I have noted before, whether to give QM a realist (as opposed to an instrumentalist) interpretation in the first place is itself a vexed metaphysical question. And since it is a metaphysical question, it is precisely the sort of question to which we can legitimately bring to bear considerations like the principle of causality. So even if there were some conflict between that principle and QM (which, as I have argued, there is not) it wouldn’t follow that we’d have to give up either. If (as I would claim) we have independent reason to affirm the principle of causality, what would follow from such a conflict is that we should take an instrumentalist rather than realist view of QM -- a position some philosophers and scientists with no Aristotelian ax to grind would adopt in any case.
An interpretation of QM that is both Aristotelian and realist will, naturally, insist that it is not the laws of QM themselves that cause anything, since they are mere abstractions from concrete systems operating in accordance with their substantial forms. Hence it is in virtue of the substantial form of a hydrogen atom that it will behave in the manner described by QM, just as it is by virtue of the substantial forms of material things in general that they will exert a gravitational attraction on one another. Now for the Aristotelian, the substantial form of an inanimate substance is not the efficient cause of its natural operations; rather, those operations flow “spontaneously” from it, precisely because it is in the nature of the substance to operate in those ways. (See James Weisheipl’s Nature and Motion in the Middle Ages for an important treatment of the subject.) Hence that a planet exerts a gravitational pull is just something it does by virtue of its nature or substantial form; it does not need a continuously operating efficient cause to make it exert such a pull. That does not mean that there is in no sense an efficient cause of a thing’s natural operations, but that efficient cause is just that which gave the substance in question its substantial form in the first place, i.e. that which generated the substance or brought it into being. It is not something that needs continuously to operate after the thing is brought into being. Hence the efficient cause of a planet’s exerting a gravitational pull on other objects is just whatever natural processes brought that planet into existence millions of years ago, thereby giving it the nature or substantial form it has. Its exerting that pull is now something it just does “spontaneously,” by virtue of its nature. (Mind you, that does not mean that it can exist or operate even for a moment without a divine sustaining cause; it cannot do so, for reasons I spell out in my ACPQarticle “Existential Inertia and the Five Ways.” But that is a separate issue. What I am talking about here is whether there needs to be some efficient cause alongside it within the natural order that causes it to exert a gravitational pull.)
Now, along the same lines, we might say that the hydrogen atom also behaves as it does “spontaneously,” simply by virtue of having the substantial form it does. Why do the electron transitions occur in just the pattern they do? Because that’s the sort of thing that happens in anything having the substantial form of a hydrogen atom, just as gravitational attraction is the sort of thing that naturally happens in anything having a substantial form of the sort typical of material objects. What is the efficient cause of this pattern? The efficient cause is whatever brought a particular hydrogen atom into existence, just as the efficient cause of gravitational attraction is whatever brought a particular material object into existence. That is one way, anyway, of giving an Aristotelian interpretation of QM phenomena of the sort cited by Oerter, and it is intended only as a sketch made for purposes of illustration rather than a completely worked out account. But it shows how QM can be naturally fitted into the Aristotelian framework using concepts that already exist within the latter.
Of course, critics of Aristotelianism will reject this way of interpreting what is going on. Fine and dandy. (Though pleasedon’t waste everyone’s time with sophomoric Molière-style “dormitive virtue” objections to substantial forms. I have explained why this objection is no good in The Last Superstition and Aquinas.) The point is that QM itself gives one no reason whatsoever to reject it. If the critics of the Aristotelian position are to find rational grounds for rejecting it, they must look elsewhere.
Newton and local motion
In the second of the two installments he’s posted since my initial response to him, Oerter raises the hoary objection from Newton’s law of inertia against the principle that whatever is moved is moved by another. Now, as I have already noted, the less misleading way of stating the principle is as the thesis that any potential, if actualized, must be actualized by something already actual. And when it is put that way, it is less obvious that there is any conflict with Newton’s law. After all, Newton’s law tells us that every body continues in its state of rest or of uniform motion in a straight line, unless it is compelled to change that state by forces impressed upon it. And how, exactly, does this contradict the thesis that any potential, if actualized, must be actualized by something already actual?
The answer is that there is no conflict at all, because (once again) the principle of causality and the laws of physics are not even addressing the same question. Now I discussed this issue briefly in The Last Superstition, and it is to what I said there that Oerter is responding. But I addressed the issue at greater length in Aquinas(at pp. 76-79), which it seems Oerter has not read. And I address it at much greater length still in my paper “The medieval principle of motion and the modern principle of inertia,” which is forthcoming in the Proceedings of the Society for Medieval Logic and Metaphysics (and which, when it appears, should be available online as well as in print).
I’m not going to repeat everything I’ve said in Aquinasor preempt what I say in the forthcoming paper, but some general remarks should suffice for present purposes. There are five general reasons why the purported conflict between Newton’s law and the principle of causality is illusory (reasons I develop at length in the paper). First, there would be no formal contradiction between the two even if they were using “motion” in the same sense. For like Kepler’s laws and the laws of QM, Newton’s law is descriptive. It tells us how a body behaves, but not whyit 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.)
Second, Newton’s law and the principle of causality are not in fact using “motion” in precisely the same sense in the first place. Newton’s law pertains to local motion specifically, i.e. change with respect to place. The principle of causality applies to change of any kind, which includes not only local motion but change with respect to quantity, change with respect to quality, and change from one substance to another. Now some might object that these other sorts of change can all be reduced to local motion. I think that is quite false, but that is neither here nor there for present purposes. For the deeper point is that when the principle of causality speaks of motion (local or otherwise) what it is talking about is the actualization of potentials. And Newton’s law simply has nothing whatsoever to say about that. In particular, when Newton’s law says that a body in motion will tend to stay in motion, it is not asserting that a potential which is being actualized will continue being actualized. Even if it were suggested that Newton’s law entails this, the point is that that isn’t what the principle of inertia itself, as understood within physics, is saying. Indeed, the whole aim of early modern physics of the sort practiced by Newton was to provide a description of nature that sidestepped the whole Aristotelian-Scholastic apparatus of actuality and potentiality, substantial forms, and the like. Modern physics didn’t offer different answers to the questions the Scholastics were asking. It simply changed the subject.
A third point is that Newtonian inertial motion is often characterized as a “state” -- that is, as the absence of any real change. Now if such motion really is a state, then there is no conflict with the principle of causality, for if inertial motion involves no real change, than it involves no actualization of potential -- in which case, obviously, it involves no actualization of a potential without a cause. Indeed, since Newton’s law says that a genuine change in an object’s local motion can occur only if a force acts upon it, the law implicitly affirmsthe principle of causality! Hence if inertial motion really is a “state,” then what Newton and his Aristotelian predecessors disagreed about was notwhether genuine change requires a cause, but only about whether local motion of a uniform rectilinear sort counts as genuine change.
A fourth point is that those who assert a conflict between Newton and Aristotle often direct their attacks at a straw man. In particular, it is sometimes thought that Aristotle and Aquinas maintained that no object can persist in any local motion unless some mover is continuously conjoined to it as an efficient cause. But in fact they denied this; their view was that an object will tend to move toward its “natural place” simply by virtue of its substantial form, and will do so even in the absence of that which imparted this form, and thus in the absence of that which is the efficient cause of their local motion. (This is related to the point made earlier about the operations that a substance will carry out “spontaneously” given its substantial form. And here too, Weisheipl’s book is the place to look for a detailed treatment of the subject.) To be sure, the idea of “natural place” is a piece of Aristotelian physics (as opposed to metaphysics) that is obsolete; and the violent (as opposed to natural) motions of objects were thought to require some conjoined mover. But all of that is beside the point. For the pointis that Aristotle’s and Aquinas’s principle of causality in fact did not presuppose that local motion as such requires a continuously conjoined physical cause.
Finally, and as all of this indicates, there can be no conflict between Newton’s law and the principle of causality because the former is a thesis of natural science and the latter a thesis of metaphysics -- or more precisely, of that branch of metaphysics known as the philosophy of nature. As Bertrand Russell and others with no Aristotelian or theological ax to grind have emphasized, what physics gives us is really only the abstract mathematical structure of the material world. It does not tell us what fills out that structure, does not tell us the intrinsic nature of the material world. But that iswhat metaphysics, and in particular the philosophy of nature, are concerned with. Moreover, the philosophy of nature, as modern Scholastics have understood it, tells us what the natural world must be like whatever the specific laws of physics, chemistry, etc. turn out to be. And the Scholastic position is that the distinction between actuality and potentiality, the principle of causality, and other fundamental elements of the Aristotelian conception of nature are among the preconditions of any possible material world susceptible of scientific study.
That is why no findings of empirical science can undermine the claims of metaphysics and the philosophy of nature. It is also why no findings of empirical science can undermine the Aristotelian-Thomistic arguments for the existence of God, for these are grounded in premises drawn, not from natural science, but from metaphysics and the philosophy of nature. Now that does not mean that these arguments of natural theology are not susceptible of rational evaluation and criticism. What it means is that such evaluation and criticism will have to be philosophical and metaphysical, rather than empirical, in nature. Nor is natural theology in this regard at all different from atheism. Atheists who think they are arguing from “purely scientific” premises never really are. They are, without exception, arguing from metaphysical assumptions -- and usually unexamined ones at that -- that are first read into empirical science and then read back out, like the rabbit the magician can pull out of the hat only because he’s first hidden it there.
Readers who disagree with these claims are cordially invited to refute them -- without either begging the question or smuggling in metaphysical assumptions of precisely the sort they deny making. Good luck with that.