# Is the idea of a causal chain physical (or even scientific)?

I am aware that the idea is venerable, going back through Lucretius to the Stoics and Epicurus, and even to Aristotle with his prime mover argument. But isn't this a pre-scientific notion? The Atomists thought that collisions cause motion. But that's only half right. Collisions are where an exchange of motion (momentum, energy) happens. A collision assumes there's already some kinetic energy--i.e. motion-- in the system of particles that are colliding. So saying collisions cause motion doesn't explain much. Of course, the Greeks didn't know all this, and it's no fault of theirs.

Look at how the concept of cause usually makes an appearance in physics. Typically, it only appears implicitly. There is talk of certain effects, like the Hall effect, the Mossbauer effect, the Zeeman effect, etc. Following philosophical tradition, and the normal meaning of the word effect, each of these effects presumably has some cause. For the Zeeman effect the "cause" is applying a magnetic field where there previously wasn't one, resulting in the splitting of atomic spectral lines. I think a fairly general definition of cause used this way in physics is a change in the degree of constraint. It could be the complete removal of a constraint, such as removing a partition that is confining a gas to one side of a container. Or it could be applying a "constraint" such as an external field.

The physical explanation of such effects is not a long list of "laws" of the form "A causes B", "B causes C", "C causes D", etc. Instead, a physical theory is developed in which the laws of evolution of the system take the form of equations (usually differential equations). You solve the equations under one constraint (boundary conditions, forcing functions, etc.), solve them again under the changed constraint, and see how the resulting behaviors are different. That is the explanation of the "effect". Physical explanations are not of the form "this domino knocks over that domino, which then knocks over this other one, which in turn..." In fact, Bertrand Russell pointed out that once you have a developed physical theory, you can completely do without talk of causes and effects. There are only regularities.

In spite of this situation, when people begin to reason philosophically, they start talking about causal chains. Maybe it's out of respect for tradition. They do it even when they are trying to be hard-nosed scientific types--trying to explain mental events in terms of physical events without resorting to dualism. And they nearly always assume that physical causes are the only kind of causes that could really matter in a scientific explanation of anything. But how can this be, when talk of causes only rarely arises in physics, and talk of "causal chains" is practically nonexistent? Won't this imprecision inevitably lead to confusion?

• Yes, causal chains better fit the archaic (Aristotelian) conception of causality, with some substances having inherent causal powers than the modern conception with laws of nature. It is closer to the folk causation talk where we single out causes from a fixed background of other initial conditions as pragmatically significant. But when it comes to mental and physical events it is easy to rephrase such talk in terms of mental and physical regularities and their relations, while the folk talk version makes the ideas more accessible. – Conifold Mar 23 at 4:16
• @Conifold Exactly. And I'm not arguing against all talk of cause and effect. I happen to think Aristotle got things basically right with his four types of cause. I am arguing against talk of causes, and especially causal chains, as if they were the epitome of physical reasoning. That's the area where they are least appropriate. If my interpretation above is right, then, in the context of physics, causes always refer to some breach of law-like behavior. A constraint is changed from the outside. The system is not quite autonomous. Perhaps there are counterexamples. – Willie Betmore Mar 23 at 6:11
• That is not what is meant in the mind/body problem discussions, at least by physicalists and dualists. "Causal chains" are just stand-ins for the unfolding of physical vs mental processes. Since most of the background is (agreed to be) irrelevant to the brain/mind relation one can collect all the relevant factors into autonomous "brain states" and "mental states", and work with a single cause/single effect toy model for them. The shorthand of "causal chains" cuts out the clutter. – Conifold Mar 23 at 7:03
• @WillieBetmore - You say - 'A constraint is changed from the outside. The system is not quite autonomous.' .This seems close to the old idea that 'collisions cause motion'. If one includes observations as collisions then this may boil down to the idea that all motion is relative. Just pondering. – user20253 Mar 23 at 10:47
• @PeterJ You're right, it is pretty similar. There's nothing stopping anyone from saying that collisions cause motion. It's not really wrong, it just isn't the physical way to talk about it. Since collisions can be accounted for within the system, then from a physical point of view they should be. But in the Zeeman effect, the "system" is a helium or neon atom--i.e. relatively simple. You don't want to have to include the human flipping the switch on the electromagnet in the system, because then it is way too complicated to model. – Willie Betmore Mar 23 at 22:29

The Atomists thought that collisions cause motion. But that's only half right. Collisions are where an exchange of motion (momentum, energy) happens. A collision assumes there's already some kinetic energy--i.e. motion-- in the system of particles that are colliding. So saying collisions cause motion doesn't explain much.

That collisions cause motion is obvious. Physics gives us a deeper and more comprehensive account, but it does not deny the obvious.

The word cause is usually not itself a scientific term, although it can be translated to scientific terms. Even with the ancients, we can see that the use of causal language is often independent of specific physical theories. Thus we can see in Cicero's On Fate Aristotelians, Atomists and Stoics debate on causal chains in the context of fate (i.e. determinism) where each party believes in a different physics.

a physical theory is developed in which the laws of evolution of the system take the form of equations (usually differential equations) … Physical explanations are not of the form "this domino knocks over that domino, which then knocks over this other one, which in turn..."

But surely even physicists occasionally talk in such terms as "A knocks over B". It is that they know how to translate the causal language, when needed, into the up to date physical terms.

In fact, Bertrand Russell pointed out that once you have a developed physical theory, you can completely do without talk of causes and effects. There are only regularities.

Bertrand Russell is indeed relevant here. He didn't just comment on the present subject, the usefulness of the concept of cause in the face of modern physics. He wrote a seminal essay about it - On the Notion of Cause (1912)

The reduction of causation to regularities (regular succession) is due earlier, in the classic treatment of causality by David Hume. It is worth mentioning that it has been argued, against this reduction, that not all regularities are causal. One classic example is the regular succession of day, night, day, night, etc. Whereas day does not cause night, and vice versa.

In spite of this situation, when people begin to reason philosophically, they start talking about causal chains … But how can this be, when talk of causes only rarely arises in physics, and talk of "causal chains" is practically nonexistent? Won't this imprecision inevitably lead to confusion?

Not inevitably. Causal talk is often useful, and precise enough. It can often be unproblematically translated into modern physical terms, where needed.

• Great answer. Thanks for the Russell link, too. You're right, confusion is evitable, but only with more care than what is sometimes exercised. I really think some people who should know better take the "physical cause" language too literally, and imagine something like being pushed into a swimming pool, or being moved around by marionette strings. And, to be clear, I reject the reduction of causes to regularities. I argued that in the physical context,causes represent a type of irregularity. So they aren't really part of the physical theory proper, which is about regularities. – Willie Betmore Mar 29 at 23:53
• "That collisions cause motion is obvious. Physics gives us a deeper and more comprehensive account, but it does not deny the obvious." There might be some ambiguity of scope here. Yes, a collision can cause motion in a body that was at rest. But are collisions the cause of motion in general? Do we have to assume an original unexplained moving particle, The Cosmic Cue Ball? It could be that the Greeks merely meant it in the obvious (and correct) sense, and I misunderstood. – Willie Betmore Mar 30 at 0:03
• @WillieBetmore Thanks. And you're right, there is an ambiguity about "collisions cause motion". Also, I don't recall a "cosmic cue ball" in ancient atomism.. so they must have assumed that atoms have initial movements which are not caused by collisions. At least for Epicurus's version of atomism, I recall that he assumed (1) that atoms move of their own "downwards", and also (2) the infamous "swerve", small random spontaneous shifts in the paths of the atoms. – Ram Tobolski Mar 30 at 18:40

You misunderstand Aristotle's metaphysics, as well as his prime mover argument.

Aristotle's prime mover:

God (the prime mover) necessarily exists. Because:

I. Something cannot be the efficient cause of itself. a) If A exists, another caused it (another necessarily caused the potential of its existence to become reality).

II. A thing's continued existence is potential, for it is not actual. b) Therefore if A continues to exist, another keeps causing it.

III. Therefore, as everything continues to exist, God (the prime mover) exists, continually and without change (if God changes from potence to act, another would have to cause Him, wherefore we conclude that God is an immutable, eternal, unchanging substance from eternity).

Now, as for the physicality of the causal chain, Aristotle's causality is metaphysical so it is above the realm of physics. His thought is not lower than current scientific thought, but in a higher and more abstract sphere.

You are confusing physical "causation" -- the interaction between physical substances -- with metaphysical "causation," or the movement of potence to act.

• But potency is not supposed to be purely metaphysical in a sense that might admit it's irrelevant to actually predicting measurable empirical changes, akin to epiphenomenalism about consciousness--Aristotelian notions of form and potency were part of a proto-scientific explanation for empirical changes like motion and organic growth, see p. 643-644 here. So if science can predict these things using mathematical models that don't involve cause or potency it's a problem. – Hypnosifl Mar 23 at 20:29
• "You are confusing physical "causation" -- the interaction between physical substances -- with metaphysical "causation," or the movement of potence to act." Tell me more about how physical causation works so I can understand the difference. – Willie Betmore Mar 23 at 22:09

I see two factors at play. First our cognitive bias to structure the world in terms of intentions, those of ourselves & others. And supervenient explanatory layers, where units in those layers are causes in their own terms, but the layer is constituted fundamentally or reducibly of the physicists world of regularities.

We learn physical skills and the use of our bodies in large part through the action of complexes of mirror neurons, which activate motor control areas in our brains from watching an action, that we would need to perform it, we mentally project our own body into the position of others for physical insight. More broadly, we learn from Dunbar's number that the close correlation for mammal species of brain size with social group size, indicates much or most of our brain development has been for social complexity, and theory of mind - and of intentions of others. Our brains are wired to make sense of the world as composed of identities with intensions. Be call the results of the intensions of others what they caused. We might expect non-social cephalopod intelligence to differ, for instance. And it's interesting to note 1 in 4 engineers have someone in their immediate family on the autistic spectrum, and that is characterised largely as an impairment of theory-of-mind.

Because it is a cognitive bias, does not mean grouping the world into identities with intensions or teleological aims isn't useful, in particular it can help make things tractable. The extreme example is predicting other humans, we accept they are made of atoms obeying laws but that is not a tractable way to interact, but heuristics like character are, and exist in a self-consistent explanatory layer with it's own terms. More generally this is very useful for learning from fragmentary data about complex systems.

Our mode of thinking about particles is to see them as like individuals, with a story. What our real understanding says, is that transformations are happening with certain probabilities, that maintain the relevant conserved quantities. A Feynman diagram is like a story, and the sum-over-histories assembles the possible stories, and that gives us insight into general behaviour.

We interpret the principle of least action, and increasing entropy, as part of the character of the universe. As we assemble the stories of systems, we picture these as causal, as having teleological intensions to maintain themselves. But fundamentally we just have patterns, and these are heuristics, which we must be careful to keep in their own relevant explanatory layer.

Noether's theorem shows us that conservation laws are symmetries under transformation, that these are dimensions. Particles are local consistencies in the transformations. The symmetries are literally a pattern, in the structure of physical laws, an efficient abstraction of experiences which narrows possibilities, making prediction forwards and backwards (far more) tractable.

'Causal' can definitely become problematic if it gets outside of it's layer. We have the pathetic fallacy, at the level of everyday experience. In science there is a huge risk of accepting a narrative explanation because it 'makes sense', which usually means conforms with our sense of the character of a system. Underestimating the impact of exponentials, and over-estimating the regularity of one off events, are known risks there. We have to actively find ways to check and counteract these biases in assembling narratives. But, identifying locii within systems and 'telling their stories' is powerfully useful.

• This is a really good answer about the role that causal language plays and how it came about (through treating nearly everything as if it had intentions). I especially appreciated the points you made about tractability, and that there are different levels of explanation/description. What is your view on talk of "physical causes" and "causal chains" in particular? Also, is the fact that causal thinking is a useful shortcut for making otherwise intractable problems tractable the end of the story? Could there be reasons why this tends to work? – Willie Betmore Apr 2 at 1:23
• @WillieBetmore: Thankyou. I see 'physical cause' as identifying a simplifying locus in a story. Consider the challenge problem of working out the function of a microprocessor, only from outside, it turned out to be nearly impossibly hard (this is to compare reverse engineering brains). Purposes hugely simplify this, the narrative of why a structure creates certain causes, links the large scale (evolution) and microscale (cells, ganglia & c). Chains I see as identifying useful locii in the transformations/iterations to pay attention to. A salience landscape, foregrounding conceptual 'nodes' – CriglCragl Apr 2 at 1:58
• That is great. It sounds as if you see causation as being closely bound up with explanation, as I do. That is why I actually kind of like Aristotle's four types of causes. Those are the types of questions that come to mind when you want to know how something got to be the way it is, and why. And it is also why I find the tendency to think of "physical causes" as being the gold standard, which obviates the need for other types of causes, disturbing. – Willie Betmore Apr 2 at 2:37
• @RamTobolski: I see that as too simplistic. Some overlays are extremely powerful. It's not about putting one set on a pedestal, or dispensing with all others. What we seek is integrity of worldview. Consider Deutsch's idea in Fabric of Reality, of needing 4 modes: epistemology, quantum theory, information theory, and biological evolution. Different modes, different languages, interoperable but separate. – CriglCragl Apr 4 at 3:24
• I like that, interoperable but separate. Your comments encouraged me to have another look at Real Patterns. It comes to similar conclusions, probably from a different angle. – Willie Betmore Apr 5 at 23:26