Downward Causation

Reading about emergence and reductionism and free will and determinism has led me to finally confront a concept I had vaguely heard about but never really looked into before: downward causation, a term that came to prominence in the 1970’s. (Some other views: here, here, here.) I think it’s a misguided/unhelpful notion, but this is way outside my area and I’m happy to admit that I might be missing something.

Physicists are well aware that there are different vocabularies/models/theories that we can use to describe the same underlying reality. Sometimes you might want to talk about a box of gas as a fluid with pressure and velocity, other times you might want to talk about it in terms of atoms and molecules. Philosophers and psychologists might want to talk about human beings as autonomous agents who do things for reasons, while admitting that they can also be thought of as collections of cells and tissues, or even once again as atoms and molecules. The question is: what is the relationship between these different levels? In fluid mechanics/kinetic theory things are pretty clear, but in the mind/body problem things begin to get murky. (Or at least, there are people who take great pleasure in insisting that they are murky.)

Reductionism notes that some of these descriptions are more complete, and therefore arguably more fundamental, than others. In particular, some descriptions are in terms of entities that are literally smaller than the others; atoms are smaller than neurons, which are smaller than people. The smaller-level descriptions tend to have a wider range of validity; we can imagine answering certain questions in the atomic language that we can’t answer (correctly) in the fluid language, like “what happens if we divide the box in half, and then divide that in half, and so forth a million times?” It therefore seems natural to arrange the descriptions vertically: “lower” levels refer to small-scale descriptions, while “higher” levels refer to macroscopic objects. The claim of reductionism is, depending on who you talk to, that the lower-level description is either “always more complete,” or “capable of deriving the higher-level descriptions,” or “the right way to think about things.”

The reductionist paradigm is of course heavily resisted in certain quarters. Emergentists like to argue that “more is different,” and that truly novel behaviors emerge at the higher levels. All the argument then becomes about what is meant by “truly novel.” Do you mean “you never would have guessed these behaviors, just by thinking in terms of lower levels”? If so, most reductionists would readily agree. But if you mean “these behaviors are truly independent from what goes on at the lower levels,” then they would not. It is not even really clear what that would mean.

Downward causation, as I understand it, is an attempt to give some oomph to the claim that higher levels are not simply derived from lower levels. Consider the good old mental/physical divide. A reductionist would claim that the mental can ultimately be reduced to the physical. (I’m gliding over various nuanced divisions of opinion in the two-dimensional parameter space of reductionism/physicalism, but so be it.) But an antireductionist might say: “Look, I can choose to lift up my hand and put it somewhere. That’s the mental acting on the physical, with causally efficacious outcomes. You can’t describe this in terms of the physical alone; the higher level is influencing what happens at the lower level.”

That’s downward causation; the higher levels acting causally on the lower levels. If you get spooked by mind/body issues, think of the snowflakes. Sure, they are made of water molecules that act according to atomic/molecular physics. But the shape that they end up taking is highly constrained by the macroscopic crystalline structure of the snowflake itself. That wouldn’t have been visible if you were just thinking about molecules; the macroscopic structure has influenced the dynamics of the microscopic constituents.

I’m doing my best to present this idea sympathetically, but it seems completely wrong-headed to me. As far as I can tell, a major motivation for thinking about downward causation is to preserve the autonomy of mental causation. We think of ourselves as intelligent beings who do things for reasons. We would therefore like to think of the decisions we make as causing certain things to happen in the physical world. But if the mental can be simply reduced to the physical, we might worry that this way of thinking is just wrong. There aren’t “really” mental states that cause things to happen; there are simply neurons and tissues (or atoms and forces) acting according to the laws of physics/biology. Choices and other mental phenomena are just illusions (according to this line of worry). Jerry Fodor put it most vividly:

“If it isn’t literally true that my wanting is causally responsible for my reaching, and my itching is causally responsible for my scratching, and my believing is causally responsible for my saying… if none of that is literally true, then practically everything I believe about anything is false and it’s the end of the world.”

Don’t worry! It’s not really the end of the world.

But before explaining why, let me give a sensible argument that downward causation can’t really work. It’s called the “exclusion argument” (if I’m understanding things correctly), but physicists would simply refer to “closed sets of equations.” The point is that, when we talk about the world in terms of atoms and forces, we have a closed system — any question we can ask in those terms, can be uniquely answered in those terms. (We have the same number of equations as unknowns.) So it can’t be true that we need to account for higher-level processes to follow things at the lower level; indeed, doing so would amount to overconstraining the system, and we would generically expect no consistent solutions. This is how we know that immortal souls require violations of the known laws of physics — those laws are complete by themselves, and aren’t able to support immaterial souls surviving past the body. My language is a little different from that in the philosophy literature, but I take it that this is what’s meant by the exclusion argument.

Why isn’t it, then, the end of the world? I think there are two mistakes being made here. One is to believe that if one phenomenon can be “reduced” to a lower level, then the higher-level phenomenon isn’t “real,” it’s just an illusion. (That’s how I interpret “literally true” in Fodor’s quote.) That’s a very bad way of thinking about the relationship between different levels. This is what I tried to argue in the post about free will and baseball: just because we can think of something macroscopic in terms of its microscopic parts, doesn’t mean that macroscopic thing becomes any less real. Baseball is real, temperature is real, free will is real — all in the sense that they are useful categories for organizing the macroscopic world, whether or not these concepts are nowhere to be found in the vocabulary of fundamental physics.

The second mistake is taking the hierarchy of levels too seriously, with some on top and some on the bottom. (This is related to the previous mistake, obviously.) I would suggest that a better mental image would feature a parallelism of levels with sideways relations between them. So we have a description of a box of gas in terms of atoms and molecules, and another in terms of fluid dynamics. These models sit next to each other, and have arrows moving sideways between them to indicate the map that tells us which configurations in one correspond to which configurations in the other. Sure, one vocabulary may be “more complete” in the sense that it accurately models a wider array of physical conditions, but so what? If another (“higher-level”) description obeys its own autonomous rules of evolution — that is, if we can successfully speak of its properties and outcomes without ever making reference to the any other descriptions (as is certainly true for fluids) — then this description is just as “real” and “literally true” as any others.

I think this way of thinking gets you everything you want. You are allowed to treat mental phenomena (or whatever) as perfectly “real” and causally efficacious. You are also allowed to attempt to “derive” the dynamical rules of one description from the dynamical rules of another plus the map between them. It might be easy, or it might be hard or impossible, but succeeding wouldn’t leech any of the power from the autonomous rules of the “derived” system.

All the mess comes when people try to mix up vocabularies across different levels. You should beware of crossing the streams — total protonic reversal could result, and that would be bad. We can talk about people as animals with minds and reasons, or we can talk about them as collections of cells and tissues, or we can talk about them as collections of protons, neutrons and electrons. It’s only when you start asking “what effect do my feelings have on my protons and neutrons?” that you start getting syntax errors.

This parallelism view gets strong support from dualities in physics. One thing we’ve learned is that you can have completely different descriptions of exactly the same underlying “reality,” but it’s not that one is lower-level and the other is higher-level; they’re simply different. Autonomous vocabularies provide powerful tools for discussing different features of the world in different circumstances. Knowing that you’re made of elementary particles obeying the laws of physics doesn’t make you any less of a person.

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44 Responses to Downward Causation

  1. JW Mason says:

    It seems like you’re simply on the anti-reductionist or emergentist side here. You and Fodor agree that talking about human beings in terms of biological or chemical processes is not necessarily preferable than talking in terms of mental states, and that in some cases there is no (useful) way of talking about mental states in terms of a “lower” or more disaggregated level at all. Where’s the disagreement?

  2. Sean says:

    [This was a response to JW’s original comment, which was completely different from the edited comment above — hopefully it still makes sense.] Depends on what you mean by “independent.” What you are pointing out is that there are many different kinds of atomic-level configurations that would reasonably be called “this post,” whether displayed on a different computer or printed out. But whenever those configurations exist, they always correspond to “this post.” And there are other configurations (random piles of dirt, or the Magna Carta) which will never correspond to this post. So they’re not really “independent.”

    It is of course possible to talk about properties of this post independently from talking about any of its physical manifestations, but that’s completely compatible with what I am saying. (Indeed it is arguably the point.)

  3. Jason Dick says:

    “Knowing that you’re made of elementary particles obeying the laws of physics doesn’t make you any less of a person.”

    Exactly! Just like knowing that a house is made of some combination of wood, stone, metal, glass, plastic, and other assorted things doesn’t make it any less of a house.

  4. Aaron says:

    JW Mason: They’re both disagreeing with a straw-man version of reductionism. Only one is taking the strawman version seriously; the other one recognizes it a creation of the Emergentists.

  5. Nullius in Verba says:

    Is the second law of thermodynamics the result of the microscopic physics of atoms and quanta (e.g. quantum irreversibility), or does it come from a higher-level boundary condition, that the past boundary of the region of study tends to have lower entropy? In this case, is the microscopic explanation the more complete?

  6. Sean says:

    JW– For one thing, I don’t think there is any such thing as “downward causation.” For another, I am completely happy with “deriving” what happens at one level from what happens at another. I don’t think this would make me a very good Emergentist. But if it does, then I am happy that we finally all agree.

  7. David Santo Pietro says:

    I have to admit that this feels like a cop out. We either have free will or we don’t. To say that free will is in some sense “real”, and at the same time admit that the evolution of physical particles allows no deviation sounds wishy washy.

    Baseball and free will don’t seem like very good analogies. Baseball exists when a collection of particles is arranged into a macroscopic state (people, rawhide, grass) which evolves according to what we classify as a baseball game. You can’t just point to a collection of particles and say that you saw free will. There are either multiple outcomes and actions available to us or there is only one. The fact that we can have the illusion of free will, if we don’t think about it too deeply is not really that comforting.

    Also, don’t we “cross the stream” all the time (in the reverse direction) when we claim that knowing information about protons and neutrons gives us enough knowledge to say where our feelings/sensations come from and what they are?

  8. Arun says:

    ““Look, I can choose to lift up my hand and put it somewhere. That’s the mental acting on the physical, with causally efficacious outcomes. You can’t describe this in terms of the physical alone; the higher level is influencing what happens at the lower level.”

    “I choose to move my hand” and the hand did not move could be because a nerve was severed or could be because the experimenter suddenly put my hand in a vise grip. I don’t see how you can avoid mixing levels; nor how you can provide a concise description of a phenomenon without mixing levels. (e.g., do I need to describe the experimenter down to her neurons and other cells?).

  9. spyder says:

    The preeminent anthropologist Jacques Maquet responded, to a seminar paper i presented, by walking up to the chalkboard and drawing an expanding spiral. He then turned and said: “No, it is not about a closed circle, nor about straight lines.”

  10. NickM says:

    Don’t overlook Downward Entailment. A tad more subtle. Google: russ abbott downward entailment.

    As far as it relates to philosophy of mind you might define human intelligence, even mind and consciousness, as a set of higher-level functions (epiphenomena kinda) emerging from the (condensed matter, in this case) physics of the brain. (Abbott doesn’t say this; it’s my own extrapolation. His paradigm is the Game of Life.)

    The relationship seems somehow interactive: the high-level functions are dependent on the physics which they nevertheless emerge to constrain. So how come this isn’t the same thing as plain old Downward Causation? Apparently it just isn’t. My mind is still working to wrap itself around this stuff.

  11. Sam Gralla says:

    This would be all well and good if anybody had demonstrated free will as an emergent phenomenon. As it is, the existence of free will in the higher-level description presents a hint of new physics in the lower-level description.

  12. Katie says:

    I’m with you until the last couple of paragraphs. Multilevel explanations are the bread and butter of the sciences (granted, some more than others). So charming references to Ghostbusters aside, it seems like the really interesting issues around reduction (at least for people happy to walk away from banal ontological arguments based on intuition and positivist fancies) are around how different levels of explanation can be integrated. You suggest rather breezily that something like Nagelian bridge principles could be used for derivation, but don’t make clear how doing so differs from crossing the streams.

  13. Whether we think of different organizational levels as layered vertically or side-by-side, there are still situations in which effects in different levels get entangled. For instance, long-distance correlations in systems can result in changes in microscopic structure, even while changes in microscopic states create the long-distance correlations. This isn’t anything spooky or non-physical, just the result of entangled causal effects between layers. Its probably a lot more common in the more complex systems we find in biology than in physical systems, but I think that’s because it’s very common in systems containing feedback loops, which are common in living organisms, even the simplest ones.

    It’s much easier to talk about this sort of thing in the context of medium-scale systems like living cells than when talking about human nervous systems and mental states, especially because we have special prejudices regarding our own mental functions. That’s why I think discussions of the nature of system organization and its relationship to reductionism tends to get derailed when we try to talk about human consciousness and psychology. Although the same discussion as it relates to animal development and the nature of genetics ran through a lot of acrimonious debate for most of the 20th century.

  14. Sean says:

    I don’t want to give the impression that I think I’ve said the last word on the relationship between different levels (although I’d prefer “vocabularies” or “theories” to “levels”). Sure, they can get complicated, and the disentangling isn’t always easy.

    I think the relevant question is: does your purported vocabulary support an autonomous understanding of properties and dynamics? That is, when I talk about fluids, I don’t ever have to talk about atoms (as long as I’m in the range of validity of the fluid description). If that’s the case, I don’t need to invoke different vocabularies. If it’s not the case, then the sensible thing to do would be to add more elements to the vocabulary until you had an autonomous model. Of course it might be very very hard to actually put together a description that is both autonomous and self-consistent as well as accurate and interesting. Science is hard! But I don’t see any argument that it’s generically impossible (although that might be true — again, this is not my area).

    The more general point remains: having a Laplace’s-Demon-level of perfect microscopic understanding wouldn’t dissuade me from speaking the language of mental states and choices, and treating them as real.

  15. Craig says:

    The problem with your exclusion principle argument is that it only applies to the physical properties of the system. It doesn’t necessarily apply to the patterns found in the system. Dennett has a nice example: Its a nice little story and I don’t want to ruin the ending, but I think it shows the limits of reductionism. Some facts about the higher level can’t be explained in terms of facts about the lower levels even in principle.

  16. NickM says:

    Reductionism probably dies anyway at the level of strong fermionic interaction (which gives rise to the Fermion Sign Problem a.k.a. the Numerical Sign Problem, N-Body Problem, Many-Body Problem, Chiral Fermions on the Lattice and a few other noms de guerre). Fermionic interaction isn’t mathematically formalizable. Computationally it’s NP-Hard. Like protein folding, it can’t be modeled, only statistically described.

    “Determinism” and “Free Will” are probably signposts of terminal ignorance. Am I the subject choosing or the object chosen? All we know is the occurrence of a choice.

  17. Craig says:

    Also I would point you to Douglas Hofstadter’s “I am a Strange Loop” where he argues that in order to understand minds you have to understand there paradoxical level shifting nature.

  18. Craig says:

    Also how are we supposed to make sense of phrases like “I turned the car key”? Is the phrase just not allowed when we are being technical?

  19. Tyler says:

    Sean, if you reject downward causation then you must also reject ‘upward causation.’ To me, this is also an argument about induction and deduction, and which approach is more valid. Put in these terms, we know that both are, yet we do have our preferences, i.e., should I build up from a particular set of empirical facts, or down from a more general principle. As we know, it is best to engage both approaches when trying to solve a problem.

    Your statement: “what effect do my feelings have on my protons and neutrons?” is like going from a pyramid’s tip to a grain of sand at its base in one leap. Though ‘extreme,’ doing so is certainly not impossible. For example, if I feel crummy I don’t exercise which increases the count in my body of a particular configuration of protons and neutrons in the form of cholesterol. Thus feeling crummy equals a specific increase in the number of my protons and neutrons, and feeling good decreases them. This is of course crude because in addition to this there are many other factors altering the configuration count of my protons and neutrons. Thus the statement, taken as an extreme example of downward causation, reveals that the relation between the items is simply more crude, but never meaningless.

    Reversing the statement in order to put it in terms of upward causation, it reads: “what effect do my protons and neutrons have on my feelings?” And from this, though again crude, we know that when a particular configuration of my protons and neutrons decrease I must also be happy.

  20. Baby Bones says:

    I think that the job of reductionism to account for novel macroscopic phenomena begins at the microscopic level and can work its way to conceptually incommensurate but nonetheless effective bigger pictures. Reductionism works well in describing how many strongly interacting systems, e.g., electrons in a metal, can behave as many non-interacting systems, e.g., a free electron gas, or be described accurately in an even more abstract way as a two-body system, e.g., an electron above the Fermi level, a hole below the Fermi level. It can accurately build up a picture wherein holes are imagined to be particles with a mass. Now these new entities effectively describe measurable quantities but are fictitious. We know that a hole is not actually a particle but it is quite valid to talk about a hole gas, just like it is to talk about the closer-to-reality electron gas.

    The thing is though, there’s lots of stuff the microscopic picture will never be able to deal with, for it involves too much complexity, whereas these bigger, yet somehow artificial, pictures can deal with the complexity. I do not think that this ability is entirely due to our ingenuity at making diagrams to account for stuff. In fact, these bigger pictures are better at explaining the nature of the phenomena than the microscopic pictures ever will be. A first-principles calculation is always going to be an vast accounting ledger that provides little insight other than to explain a mysterious aspect to a bigger picture or to confirm the validity of the bigger picture in a simple case.

    As this is a general state of affairs in science, I suppose there is a general principle at work and i will say it is called “decoupling microscopic pictures from macroscopic pictures”, and there is reality to both pictures.

    I guess essence for me is the opposite of its normal definition. To me, it is what effectively happens, not what lies underneath; in other words, the essence of the matter is not the essence of matter. Hence, people are free agents, and statements to that like can be formulated free of atomic considerations once you can eliminate certain couplings from consideration (usually, they mostly cancel out).

    In my opinion, psychology can be completely decoupled from physics (one day, scientists will renormalize psychology), but we have yet to find a way do so with consistency, and it is as yet a fruitful an endeavor to consider the physics of neurons and neural networks.

  21. Bee says:

    Your argument about the # of equations and unknowns becomes a little wobbly if you have an infinite amount of both. What’s the number of constituents of a baseball? I’m also not sure the distinction between micro- and macroscopic as being a matter of size is waterproof. Anyway, that’s not to say that I disagree with you.

  22. Sean, I sometimes fantasize that the way to dissolve all debates about reductionism vs. holism would be to teach everyone computer programming! But then I remember that that can’t be the whole solution, because programmers get into these debates too.

    Seriously, while there are lots of really terrible “anti-reductionist” claims — some of which you demolished in this post and previous ones! — there’s ONE “anti-reductionist” claim that I’ve been able to make sense out of. This is that, not only do there exist “effective” higher-level laws that everyone uses in practice, rather than rederiving everything from the lower-level laws — an obvious point that any reductionist would agree with — but many of the higher-level laws would very plausibly be the same, even if the lower-level laws had been different.

    So for example, we could easily imagine Darwinian natural selection operating in a universe with completely different laws of physics than ours. But if so, then in that specific sense, we could think of natural selection as enjoying a sort of “autonomy” from lower-level physics. By analogy, if I run a Java applet on my PC, it doesn’t seem right to say that the “true, lowest-level description” of the applet resides in the machine-code instructions that my PC actually executes, the Java bytecode being merely a “higher-level description” of what’s going on — since exactly the same Java bytecode could also run on (say) Mac or Linux, in which case it would correspond to completely different machine code.

    (Saul Kripke made a similar point in his famous book Naming and Necessity, where he asked questions like: “would water still be water if it had turned out to be something other than H2O?”)

  23. A good, no-nonsense description of various levels, their relationships among one another, emergence etc (among many other things) is to be found in Robert Pirsig’s book Lila. I recommend reading his first book beforehand, namely Zen and the Art of Motorcycle Maintenance. (As Pirsig himself says, don’t take the title too literally. In the same spirit as acronyms for physics experiments, having a nice ring to it is more important than having it be a good description of the thing it titles.) Even if one doesn’t agree with everything in his books, a) they are still a good read and b) they are a good summary of various aspects of science and philosophy which are not found together in many other places.

  24. @22: Good point. Pirsig gives a similar example in one of his books: Give someone with a knowledge of electronics all the tools he wants and a hard disk. Task: Find the novel residing in a text-processing system on the hard disk. While in some sense the novel is, of course, there and could, in principle, be found (though in practice this would probably require a knowledge of the operating system, the text-processing program and the hard disk, in addition to a general knowledge of electronics), most would agree that that is merely one possible representation of the “ideal” novel (I hear my thoughts echoing inside of Plato’s cave now) and hence that the description of the novel per se is, in this case, more fundamental than its representation.

    Of course, Abstruse Goose hits the nail on the head with regard to the relationships between levels: .

  25. “So for example, we could easily imagine Darwinian natural selection operating in a universe with completely different laws of physics than ours.”

    An interesting spin on this is James P. Hogan’s book Code of the Life-Maker; highly recommended. (For the record: I grew up on Asimov (whom I met personally once) and Clarke and could never really get into most other s.f. (I was not impressed by, say, Heinlein’s Stranger in a Strange Land (though it is a great title). Some of Hogan’s books are quite good, some are OK. There are probably some which I haven’t read which aren’t good at all. (Of course, we all know that Wagner’s music is better than it sounds and one should, at least in some circumstances, distinguish between the artist and the art. In particular, anyone who finds Hogan rather unpalatable as a result of relatively recent public statements can rest assured that there is no hint of this in his books, at least in the earlier ones (which I have read).) I am not ruling out the fact, though, that there might be other s.f. writers, young or old, who are worth reading for me.)