(this post has been edited on 14 Nov 2023 based on comments received at the time)
Question
Emergence is widely discussed in the context of what could be called bio-philosophy ("Where does life come from?") and existential philosophy ("What is consciousness?"). The concept is invoked to save physicalism from its reductionist contradictions and conjure up a physicalist world view where life can sprout out of a primordial soup, and where animals can play Beethoven's 5th.
A belief in some inherent capacity or propensity for emergence in this world, is supposedly all it takes to explain how one can get from a primordial soup to a symphony (and other cultural goods) in 4 billion years, without using the easy cop-out of a god of the gaps.
In spite of its good fortune, the concept is rarely examined philosophically, to my satisfaction anyway. One of the recent contributions there, by Mark Bedau, was to propose a distinction between weak and strong emergence. This distinction never resonated with me, in part because I don't see that it makes a real difference, and also because I suspect it's a sort of ploy to dismiss the very concept of emergence. (details follow)
So I am asking the double-barreled question: Is the distinction between weak and strong emergence conceptually clear, and if yes, does it make any significant difference?
Definitions
I haven't found a definition of emergence in the relevant SEP entry. Wikipedia proposes the definition by G. H. Lewes, who coined the term "emergent" in 1875, distinguishing it from the merely "resultant":
Every resultant is either a sum or a difference of the co-operant forces; their sum, when their directions are the same – their difference, when their directions are contrary. Further, every resultant is clearly traceable in its components, because these are homogeneous and commensurable. It is otherwise with emergents, when, instead of adding measurable motion to measurable motion, or things of one kind to other individuals of their kind, there is a co-operation of things of unlike kinds. The emergent is unlike its components insofar as these are incommensurable, and it cannot be reduced to their sum or their difference. (emph. added)
So according to the concept inventor, Lewes, emergence is about what in a system is "more than the sum of its parts" (Aristotle).
To define what he calls "strong emergence", Bedau does not start from Lewes' definition above, but from the "clearly articulated and carefully defended account" by a certain Timothy O'Conner, who defines emergence via the capacity for the emerging stuff to exert downward causation on its elements.
However, downward causation is a higher bar than that set by Lewes, arguably. This may be why Bedau choses O'Conner's definition of emergence tout court for his definition of strong emergence. Another reason is perhaps that his real beef is not with emergence proper, but precisely with the concept of downward causation.
In his essay, he writes of “strong emergence” (i.e. emergence as understood by O'Conner and others) as magical thinking.
Here is how Bedau defines the concept he proposes instead in his essay, weak emergence, which to him his "metaphysically benign":
Macrostate P of S with microdynamic D is weakly emergent iff P can be derived from D and S's external conditions but only by simulation.
Why "only by simulation"? Because Bedau is having in mind a chaotic system, that can "only be simulated" through models and not resolved with a unique mathematical solution. Specifically, he seems to have based much of his idea of weak emergence on the phenomenon of cyclones. A cyclone does not, in his view, exert downward causation, thus it is only weakly emergent.
So is Bedau saying that cyclones are “weakly emergent” “while living beings are “strongly emergent”, then? No, he does not. What he is really saying is that strong emergence (when defined as downward causation) is magic thinking, and thus cannot logically exist as a real physical phenomenon. According to him, you and I are just as weakly emergent as hurricanes.
In other words, to use Lewes’ terminology, he is saying that everything is resultant, nothing is emergent. Nothing ever emerges.
Reflexions
To me, this argument has a number of holes:
Bedau falls well short of defining a new, alternative concept. He merely waves in its general direction, since his ‘definition’ of weak emergence is in fact a condition to verify in order to qualify, not actually a descriptive definition of what the concept means. Apart from being "metaphysically benign" and only amenable to simulation, we are left in the dark as per what this phenomenon exactly is, and have no clear, usable notion of emergence at the end of his essay. So his work leaves us poorer conceptually than where we started from.
He fails to address the power of the feedback loop concept, which implies that high-order, large effects can in turn become regulating causes for what originally affected or created them. This concept is very useful in biology, and is often conceived of as combining downward and upward causation, for instance in population genetics when speaking of ecosystem pressure. So when Bedau argues in his paper that "strong emergence" is not a useful concept in science, he is probably ignoring biology entirely.
To my mind, emergence evokes a slow, progressive growth. It starts small and then it grows progressively. So from that angle, I find the distinction between the weak and strong kinds not germane to the concept. The distinction could prove quantitative rather than qualitative: with time, weak emergence will grow strong...
Indeed, another side of the concept is that this "growth" should build something semi-stable. If something emerged, it's there to stay, at least for a little while. A blip on a screen, that goes on and off in a millisecond, does not really "emerge". There is a certain resilience assumed in emergence.
Hence perhaps O'Conner's definition: is truly emergent what is resilient, what can defend itself against entropy, the force that ultimately destroys all things. This implies the effectiveness of emerging systems (like living organisms) to act causaly for their self-preservation and maintenance. Aka what people call "downward causation".
- Arguably (many of the comments to this question refer to that point), the concept of "downward causation" itself is poorly crafted, and thus does not offer a good criterion upon which to define emergence, as O'Conner tried to do, followed by Bedau.
Emergent phenomena emerge out of something, so the concept also calls upon the idea of a background, against which or rather thanks to which a certain thing can emerge. The emerging stuff, if widely replicated, can in turn constitute a new background, upon which another, different kind of emergence may happen. In this sense and as stressed by Ted Wrigley, the emerging stuff both depends on the background and acts on the background. So the phrase “downward causation” is poor wording. The actual idea is intractably reflexive, i.e.:
• small-scale local interactions produce large-scale systemic (emergent) phenomena, and…
• these large-scale systemic (emergent) phenomena affect those small-scale interactions. [I thank Ted for this section]
Another commentator, @Conifold, stressed the idea of causal closure, expressed as follows: “microphysics do not change in collectives”. From this argument, there ought not be anything like “downward causation”, or “upward causation”. There’s just causation.
I agree that physics do not change in collectives, so I accept causal closure. I accept that, when biologists speak of "environmental pressures" it is merely a way of speaking, that animals live or die because of specific things that kill or sustain them. A particular virus got them sick, and then a particular predator ate them, for instance. Nobody ever died of something as general as an "environmental pressure". And yet, we speak of epidemics and we study them. It's a useful manner of speaking.
After all, "upward" and "downward" are subjective terms, in the eye of the beholder. Nature is one, and not divided into levels outside of our mind.
However, I see no contradiction in including steric effects among my cause-to-effect thinking. Stericity is about the shape that chemicals take, eg proteins. This shape is causal, and it is additional to the mere components of a protein, in the sense that one can make different proteins with the same aminoacid components. Certain precise shapes or configurations of elements have the capacity to make microphysics do things that other shapes or configurations cannot do. For instance, the manner in which the components are inserted on a mother board -- their configuration -- will have an important impact on the functionality of any electronic device.
I thus propose to speak of the causal power of structures (including in terms of resilience, i.e. the capacity for self-maintenance and preservation), instead of speaking of “downward causation”. This is intended as more precise wording for the same idea: the idea that certain systems / structures / shapes have different effects than others.
I further propose to base the concept of emergence not on “downward causation” but on the causal power of the emerging shape, including in terms of its resilience power (its capacity to dynamically maintain itself). The stronger this causal power, the stronger the emergence, in coherence with my gradualist view of the concept.
Looking forward to further discussion.