Materialism done right: my review of Aristotle’s Revenge in one post

The original posts at the Orthosphere are here, here, and here.

Importance of a philosophy of nature

There is an impression in some quarters that scholastic philosophers and theologians are always stepping on scientists’ toes, trying to shut down investigation of empirical questions with sophistical a priori arguments. I think if anything, scholasticism’s failing has more often been the opposite–a great retreat into metaphysics, into principles that, being supposedly valid in any possible universe, can tell us nothing about the one that happens to exist. While this does protect against “Galileo affairs”, there is the danger that we will not know how to apply the general categories of “substance”, “potency”, etc. to the world we experience and have revealed to us in science. And concepts we cannot apply, we don’t really understand.

The other danger is that, without a thought-out metaphysics as guide, we may read into scientific theories an unexamined metaphysics and recapitulate ancient fallacies. Science is the fullest and most systematic exposition of our experienced world. We do want to read our ontology out of it, but how to do this is neither obvious nor easy, and we need the help of general metaphysics.

Thus, the American Thomist Edward Feser’s philosophy of science book, Aristotle’s Revenge, is to be welcomed, whether or not one agrees with his conclusions.

Transcendent Laws vs. Causal Potencies

Why think that Aristotle would be a useful guide for reading ontology out of science? I became convinced of it when I noticed that people, scientists and nonscientists alike, mean two different things when they say that the laws of physics explain such-and-such. One view, the sensible one I would say, is that laws of physics are descriptions of how the sorts of things that happen to exist behave. But I have noticed that sometimes laws of physics are treated as universe-transcending causal agents, as for example when they are said to enable the universe itself to come into existence out of “nothing” (another grievously misused word). This is in fact the error of Plato, who also put the loci of intelligibility in a transcendent realm, and physical laws conceived this way face all of the same interaction problems. Aristotle solved the problem in the only way possible, by relocating the forms into the physical world, and we must do the analogous thing with physical laws.

Feser explains this pretty well in his previous book Scholastic Metaphysics by retrieving the concept of potency. He notes that contemporary analytic philosophers have themselves reinvented the concept under the name “physical intentionality”, and Feser argues pretty convincingly that it can’t be reduced to actual structure if one is unwilling to appeal to transcendent laws of nature.

Suppose A is potentially X but actually Y. A is not actually X, but A being X is more than a counterfactual statement:  counterfactuals are statements; potencies are the beings that ground such statements.  Let’s apply this to my problem. Consider a system in classical mechanics. Its actual state is a point surrounded, one might say, by a phase space of possibilities. The phase space contains structure (a symplectic 2-form, a Hamiltonian) which, to do their work, must be defined in the nonactual space. (They would be senseless if only defined at the actuated point.) The Aristotelian solution is to assign a sort of reality (potential being) to unoccupied state space to represent the nature of the system and to be where the “laws of physics” live.

Naive attempts to read ontology out of science often end in metaphysical extravagance. Other examples of this come from attempts to relegate features of the manifest world exclusively to the mind. Early modern discourse on “secondary qualities”, when it was falsely believed that physics does not recognize the reality of color, heat, and other non-geometric qualities, is a case of this. So too are claims that intentionality and teleology exist only in the mind. The trouble with this is that if the mind contains things not in the material world, then minds must be mysterious, immaterial things.

I support the modern prejudice that philosophy should not need to posit immaterial metaphysical constructs–Platonic forms or immaterial souls, regardless of whatever names these hide under–to explain the material world. The claim I shall investigate is that Aristotelianism-Thomism is materialism done right.

Images scientific, manifest, and metaphysical

Feser endorses structural realism in a general way, without accepting any narrow version of this position that reduces scientific knowledge to triviality. One suspects that with this label Feser mostly means to endorse my starting points above: science gives us real knowledge about the world, but ontology can’t just be read off its surface. In Feser’s case, there is also a strong emphasis on the supposed incompleteness of physics, or of scientific reductionism more generally.

I would like to clarify the assertion that physics gives an incomplete picture of the world, because many philosophers make such claims, but they can mean very different things. I will concentrate on the possibility that physics misses information about the material world, granting as obvious that physics has little to say about things like ethics and religion that are beyond its purview. The most modest and popular antireductionist claims are of the “missing the forest for the trees” variety. Even if one could predict the behavior of machines, people, and animals by evolving all of their molecules, one would miss out on the macroscopic categories (function, motivation, etc) that provide a distinct layer of intelligibility at this level. Thus, philosophers speak of irreducibly new phenomena emerging from the lower level. It’s not clear, though, that any reductionist would disagree. Some of Feser’s arguments are of this kind, e.g. that to explain themodynamic or macroscopic chemical phenomena, the explanation must refer to those phenomena and thus be cognizant of the macrolevel. This is true, but it takes one no farther than forest/trees anti-reductionism (i.e. emergentism).

A more radical claim would be that the laws of physics are actually wrong and don’t apply outside of the highly controlled situations in which scientists test them. This is Nancy Cartwright’s position, but her examples are unconvincing. Feser flirts with this idea, but the main thrust of his argument is that physics is incomplete because it is an abstraction of reality, and abstractions necessarily leave things out. No doubt, physicists routinely discard “irrelevant” details in their explanations, but the claim that physics necessarily leaves out information about the physical world is a radical one.

It does nothing against Feser’s claim to point to the astounding reliability of physics, because physics could be perfectly reliable in its own order while completely ignoring features outside this order. However, if claims of the limitations of physics are to be more than gestures of epistemic humility, we must have some independent source of information.  Feser sometimes thinks he can get this from our manifest image “common sense” experience/conceptualization of the world, but I find this questionable.

For example, in a section on secondary qualities, Feser rightly objects to claims that color is a mere subjective experience. Physics has clearly established that color is the wavelength of visible electromagnetic waves. But Feser dismisses this account of color as not being “color as common sense understands it”, so that the world of physics is still in some esoteric way colorless. I do not understand this at all. Common sense is not an understanding of light rival to that of optics; it’s not an understanding at all, but a bare experience of it. The qualia of colors (the only thing physics clearly does not provide) have no independent structure, which allows us to identify them simply as the experience of light at different wavelengths. The color of physics, meanwhile, explains all our experiences of color: the blueness of the sky, the order of colors in the rainbow, the red glow of a hot stove… What else is there?

Feser also does not believe that physics captures the reality of change and temporal succession. Again, the claim will seem odd at first, since in physics we often encounter cases of something. Is that not change? Feser replies that physics ignores the difference between space and time, that it only recognizes “static change”, which fails to capture time “as common sense understands it”. Here I would partly agree and partly disagree.  It is not true that temporal succession is no different in physics than spatial adjacency. Spacetime has a definite causal structure, encoded in the metric, so that one can unambiguously say whether two events are timelike separated and hence that one could influence the other.  Only spacelike hypersurfaces are Cauchy surfaces.  Nor is a moving object at an instant of time static: it is perfectly sensible to have even though as .  (If you find something metaphysically suspicious about limits, re-express in terms of the tangent space at a point.)

On the other hand, the situation of time is in some ways opposite to that of color. The aspects of “manifest time”–spatially separate simultaneity, “flow” from the past to the future–are not direct experiences but a sort of first-order conceptualization. I will later argue that physics’ conceptualization is superior in adequacy to experience, parsimony, and internal coherence. For now, I’ll just point out that pointing to the experience of change does no damage to the physicist’s spacetime picture, because that I have different experiences at different events on my worldline is expected on the physicists’ picture too.

A brief history of the debate on space and motion

For an excellent treatment of the substantivalism/relationism debate, I recommend Paul Earman’s book on the subject.  Newton famously argued that space and time exist independently of anything filling them, while Leibniz countered that only spatial relations between objects are real. These arguments were long tied to the question of motion. Leibniz pointed to Galilean invariance to argue that there is no absolute standard of rest, while Newton countered with is bucket experiment, showing that water in a spinning bucket certainly knows that it’s spinning. The motion debate was only satisfactorily disentangled in the 19th century; in modern terms, we would say that spacetime has affine structure but no favored timelike vector field/congruence, i.e. acceleration but not velocity is absolute.

General relativity ironically provided the most powerful arguments to both substantivalist and relationist camps. Einstein’s spacetime retains its affine structure but also aquires its own dynamical degrees of freedom (the two polarizations of gravitational waves), which certainly seems to lend it independent reality. On the other hand, the general covariance of the theory is often taken to suggest that we not assign any real identity to spacetime points, and Earman has used Einstein’s hole argument, arising from this diffeomorphism invariance, to restate Leibniz’s argument without the latter’s questionable theological assumptions.

Aristotle and his disciples on motion

Aristotle, in his Physics, presents a definitely relationist account of space and time, going so far as to believe that spatial placement would be meaningless without matter filling space, and time would not pass without something changing. Carlo Rovelli praises Aristotle highly for his relationism, for relationism is still a strong contender in the philosophy of science, and so for once Feser could have stayed within the mainstream while following his master. But he does not do so.

Feser helpfully reviews the scholastic literature on locomotion, showing that the principle of inertia is not necessarily a problem even if one limits oneself to Thomism. (Dun Scotus had no problem with self-motion.)  The goal, though, is not to defend scholasticism but to understand motion.  Feser entertains several hypotheses. To mention only two, there may be a quality called “impetus” (which would break Galilean invariance) or that motion is relative and hence a “Cambridge property”, and thus not real enough to need a cause.  This latter idea is interesting, since it amounts to using Bertrand Russell’s critique of Aristotelian logic (that it can’t handle relations) to defend Aristotle’s physics. However, a relation between A and B is a property of the system A+B, so denying motion is real change would have to be combined with some rule limiting allowed aggregations.

Feser unfortunately quotes a number of foolish arguments by Colin McGinn against Galilean invariance.

“Consider a universe with just two objects, A and B [moving with respect
to each other]…For B to move, then, is for it to be at location L1 at
one moment and at a different location L2 at the next. Now, since B is
indeed moving from A’s frame of reference, the locations L1 and L2 that
B is at at each moment must be different locations. But since B is not
moving from B’s frame of reference, the locations L1 and L2 that B is at
at different moments must not be different locations. So L1 and L2 are both identical and not identical. But that is absurd.”

Well, the whole point of Galilean relativity is that there is no unique way to identify the same points at different times. Different frames will do so differently. Coordinates are just labels. Thinking otherwise “begs the question” against relativity, to use one of Feser’s favorite phrases.

“If we are considering only their motion, we could say that either the sun is at rest and that the earth is moving relative to the sun, or that the earth is at rest and the sun is moving relative to the earth. However, when we factor in the different masses of the sun and the earth, this is no longer the case. For given its far greater mass, the sun exerts a gravitational pull on the earth that is much greater than the pull that the earth exerts on the sun. Hence it is the sun that is causing the earth to move relative
to itself, rather than the other way around.”

Presumably McGinn meant that the acceleration of the Earth is greater because its mass is lower, since obviously the force of the Earth on the sun is equal in magnitude and opposite in direction to the force of the sun on the Earth.  Still, this is Newton’s bucket velocity vs. acceleration stuff, hardly news or a problem for Galilean relativity.  Interestingly, in general relativity, both the sun and Earth have zero acceleration, and we must invoke a preference for stationary, asymptotically flat metrics to favor a coordinate system in which the sun doesn’t move.

The continuum

We have seen that modern philosophers of physics have come around to the suspicion that spacetime is not just an infinite collection of points, that in fact the actual existence of points is more dubious than that of finite regions. The ancient Greeks got there first. Feser gives a review of this in terms of Zeno’s paradoxes. This is the historically correct way but may put off modern readers who will see fairly easily how Zeno is taking limits improperly to get his incorrect zero and infinity answers. (See Russell on the intuitions that were probably driving Zeno and how the modern theory of infinite sets, even more than calculus, answers them.)  A better way, I think, would be to note that even in mathematics, a line is certainly not just an infinite collection of points. In addition to points, there is also a topology, a sense of neighbors. We often take take this for granted because all the lines we draw are embedded in a metric space, which supplies a natural topology. It is, however, an independent ingredient. A line is a one-dimensional topological space, and the topology and points are related in a way vaguely reminiscent of form and matter. Aristotle’s formulation of this is that the points exist only “potentially”. That the points in a line are somehow not actually there is a strange claim, but the holist intuition driving it is certainly defensible.

Time and causal structure

As Reichenbach has explained, even if the scientific theory of relativity were to be disproved, the epistemological theory of relativity would still stand. Given a maximum communication speed, there is no unique way to decide that two events separated in space are simultaneous in time. Indeed, the special theory of relativity predicts that the time order of spacelike separated events is frame-dependent. Behind these epistemological and scientific points is a deeper ontological lesson. Time is the order of causality. Past events are what we remember; future events what we can affect.  Absent the possibility of causal influence, two events should not be relatable by the order of time. Significantly, it is the network of possible causal relations between points–given by the light cone structure–that gives Minkowski spacetime its natural topology.

Whenever I read a philosopher arguing that the theory of relativity has not made presentism untenable, I come away more convinced than ever that relativity has indeed made presentism untenable. One must posit a preferred foliation of spacetime that has left no trace on the laws of physics or human experience, or one must hold out hope that some future physics will provide such a trace, or one must define the “now” counterintuitively using arbitrarily selected special events. Additionally, I think the truthmaker objection to presentism is stronger than Feser gives it credit for, but as a traditionalist I may be too sentimentally attached to the reality of the past. Feser’s mostly grammatical arguments didn’t convince me, but he does make one very strong point. Namely, that it won’t do to say that change as common sense would recognize it is not real but exists only in the mind, because if it exists in the mind, then it exists. The eternalist absolutely must establish that change as he understands it is sufficient to explain everything about the human experience of the distinctive character of time. For a recent attempt by the eternalist side to do this, I recommend Craig Callender’s book.

It is the mark of the Aristotelian to return what modern philosophers have said is only in the mind to the objective physical world, whether by insisting that these things really are in the world as revealed by physics (my usual strategy) or by emphasizing features of the world not captured by physics (which is more often Feser’s strategy).

Quantum mechanics

Probably no development in physics has deeper metaphysical implications than quantum mechanics, although it is not yet clear what those implications are.  Classically, we are used to a subject’s having any property to be either definitely true or definitely false, not linear combinations, not relative to an observer or a “framework”. The subject/predicate relation has been at the heart of logic since Aristotle, and indications that our understanding of it needs to be broadened are exciting to scientists and philosophers alike.

Heisenberg himself pointed out that indeterminate properties in his theory are reminiscent of Aristotelian potencies. In his book, Feser reports speculations by scholastic philosophers to the effect that matter at small scales is somehow closer to prime matter than macroscopic substances, that it is therefore expected to be less determinate, less actual and more potential. Their arguments to this effect are rather unclear, but perhaps we can do better. I would not say that elementary particles have more potential in the sense of freedom of possibility. The Hilbert space of a single particle (assuming, for the moment, that the particle is in a pure state so that its state is a vector in this space) is small compared to that of a many-particle system. Nor is the indeterminacy of an elementary particle (e.g. ) necessarily larger in an absolute sense–the uncertainty principles apply to all objects–but it is generally larger in a relative sense.

Let’s try to make this more explicit.  For an object of mass m and proper lifetime T, one could define a relative indefiniteness of action by , which seems reasonable enough, although something else would be needed for massless particles/fields.  On the other hand, if one works from some objective collapse interpretation of quantum mechanics, the task is much simpler.  Definite things are those that have whatever it is that triggers wavefunction collapse / state vector reduction.

The most interesting aspect of these speculations is that they invite us to reconsider Leibniz’s task of connecting Aristotelian categories directly to mathematical structures in physics.

Parts and wholes: is water ?

It is a very deep belief of the modern mind that parts are ontologically prior to–“more real than”–their wholes.  And yet, this is not a result of any scientific discovery but just a largely unquestioned metaphysical prejudice. Thomists claim rather that wholes, when they constitute substances, are ontologically prior. They frame this priority in terms of the potency/act duality: the composite substance exists in act, its components merely virtually or in potency.

Thus, in water (Feser’s example), hydrogen and oxygen exist but only in this attenuated sense.  David Oderberg argues for this understanding by noting that water lacks the distinctive properties that accompany hydrogen and oxygen, implying that they are not present in act. As an argument against atomism, this doesn’t work. Atomists do not claim that water is made of hydrogen (which they regard as the gas that is an aggregate of molecules) and oxygen (the gas that is an aggregate of molecules) but that water is an aggregate of molecules, and it is not clear that the hydrogen and oxygen atoms do not retain sufficient essential properties to be identifiable within individual molecules. However, Oderberg’s point is also intended as a criterion that substantial union has been achieved to those who accept such categories. More generally, substances are said to have powers and properties that are irreducible to those of their components. Of course, atomists who endorse the phenomenon of emergence also accept irreducible emergent properties, so this observation is really not as controversial as the metaphysics in which it is embedded.

It sounds strange to hear that the components of my body (molecules? cells? macroscopic organs?) exist in only a “potential” or “virtual” sense. Not more, though, than the mainstream view that I myself exist only nominally, that in reality there are only excitations of quantum fields. Why look for ontological priority at all? Why not say that my atoms exist, that I exist, that all existences are on a level, and have that be that? For the Thomists, the motivation is sometimes given that the unity of substances must be properly acknowledged. Both Aristotelians and atomists seem to be worried that putting all existences on a level would mean double counting, multiplying beings unnecessarily in the mind.

Teleology in the living world

That eyes are for seeing and hearts are for pumping blood would seem to be uncontroversial scientific facts. but if one is committed to a view that teleology doesn’t really exist in nature, one will be driven to find some way of explaining the apparent functionality of biological organs.  The most popular today is to appeal to natural selection–the function of an organ is what caused it to be selected for.  Feser shows that this criterion is subject to indeterminacy problems; in some cases, a number of non-equivalent descriptions would all meet the claim to be the function.

However, I think his first, simpler argument is more decisive. The function of a thing cannot depend on its history. If the first human being had suddenly popped into existence fully formed five minutes ago, that would surely not change the function of the human eyes and heart.  Clearly, causation actually works the other way, e.g. eyes were selected for because they are for seeing, which is an adaptive skill.

As Feser has argued many times, pushing non-mechanistic features into the mind is not a viable long-term materialist strategy, because it just makes the mystery of the mind completely intractable. To use the delightful analogy from his blog, the strategy of sweeping dirt under the rug is guaranteed to fail when the time comes to clean under the rug.

Conclusion: giving the world its due

I have argued for Aristotelianism-Scholasticism as materialism done right, but this might now seem to have been a bait-and-switch. We have made due without Platonic Forms and Cartesian egos, but we have ended up acknowledging final causes in nature. And there is more. By making the laws of physics immanent in nature, we have captured well the universe as it appears through the scientific method–as an ordered and intelligible but radically contingent being, a combination most naturally explained by invoking a transcendent creator Deity.

Could we by a similar move attribute the features of God instead to nature, say to man, as Feuerbach insisted? We could not. Denying the contingency of the world goes against the premisses of the scientific method, because if all beings are necessary, observation and experimentation are unnecessary.  It goes against the formalisms of mathematical physics, all of which involve an act/potency, state/state space split. To deny contingency would be to make the connection between mathematical structure and the subject in which it is instantiated necessary, which would tend to reduce the latter to the former, to a large extent removing the materiality of matter. By offloading pure actuality onto God, we let material beings be material beings.