I have been having a metaphysical debate on Twitter, which is more surreal than reading the Tractatus. My interlocutors said a few things which leads me to want to clarify my views a little more than Twitter allows. Hence…
My thesis is this:
Emergent properties are no different, ontologically speaking, than any other property. They consist solely in their surprisal value.
This is perhaps plain enough to those who know the literature, if a little simplistic. Those who do not spend their says poring over philosophical papers and books may find it a little opaque, so I will try to explain in plain language (or in technical language where I can explain that) what the issues are and what I mean by it.
Emergence is a hot topic of the past two decades. It was the subject of at least five books by that title, and each one made claims that emergent properties are critical for understanding, and explaining, the complex world of biology, society and information technology. I agree that it is crucial to understanding these things, and basically any dynamic system. What I dispute is that it explains them. To begin with, then, we have to ask, “what is emergence?”
John Holland defines it as “much coming from little” in complex adaptive systems (a phrase he coined to describe things that are, well, complex, adaptive and systems, all of which require much further definition). In Bedau and Humphreys’ edited book they note that emergence is often defined with a number of ideas: irreducibility, unpredictability, conceptual novelty, ontological novelty and supervenience (p3). It’s an interesting list. Some of these are epistemic and some are ontological. One (unpredictability) may be both. Further, the term “emergent” is sometimes applied to phenomena, to properties, and to objects and processes. Again, there is an ambiguity whether we are talking about our epistemic states (an emergent phenomenon is one we did not expect to see occur given what we know of the constituent substrate), or ontological facts (an emergent property is one that cannot be reduced under any circumstances to the properties of the constituent substrates and their relations).
Moreover, there appear to be several other claims: emergence is relative to a theory, it is the denial that physics is the most basic science, it means we cannot reduce some domains (almost always human minds, often also biology) to physics, etc. So the so-called “emergentist thesis” is a very slippery beast.
Philip Clayton has a very nice short summary of what the emergentist thesis is typically taken to be. There are four theses (taken from el-Hani and Pereira 2000): ontological physicalism is denied – what there is includes more than the physical; property emergence is asserted – genuinely novel properties emerge in complex systems; the irreducibility of the emergent is asserted – emergent properties are irreducible to, and unpredictable from, the lower-level phenomena from which they emerge (often put as “the whole is more than the sum of its parts”, also known as holism); and downward causation is asserted – higher-level entities causally affect their lower level constituents.
Each of these admits of several alternates. For example, one might not be a physicalist but still be a monist (presuming physical stuff and, say, mental alike to be different instances of some metaphysical “gunk”, to use Lewis’ term. One might allow that properties emerge novelly, but that they are still physical properties (which means, in this context, something that can be fully described in the language of an actual or ideal future physics). One might think that irreducibility is due to our inability to get the information and knowledge or theory needed, or that it is a limitation of our computational skills. Downward causation is, however, where I think the real issues lie and so I will discuss that shortly.
First, let us consider what it means to “reduce”. In biology, reductionists are akin to baby-raping robber barons. One of the worst things one can say of another in a biological context, whether in the sciences or the philosophy of the science, is that one is a reductionist. The term has been badly abused and confused. It usually means that one thinks something precious (like human cognition, behaviour or morality) can be “reduced to” genes, where “reduced to” means “is eliminated by”.
In fact, to reduce a theory to another is regarded as a good thing in science, generally. When it was first introduced by Ernest Nagel in 1961 (chapter 11), he defined it as
the explanation of a theory or set of experimental laws established in one area of inquiry, by a theory usually though not invariably formulated for some other domain. [p338]
Reduction is a case of explanatory economy, in which we make do with less in the way of theoretical apparatus to explain more than we used to. The trouble was, reduction quickly got tied into a view of domains that we can call the “layer cake” view, which is sometimes called the hierarchy view of ontology. According to this, physics supports chemistry, chemistry supports biology, biology supports psychology and sociology, etc. The idea then is that we can reduce mind to biology and thence to physics. But it doesn’t follow that we must do this. I personally think that reduction is flat: everything reduces to physics more or less directly. The layer cake is of our own construction.
This bothers some scientists: it implies that we should effectively make the discipline of biology the servant of physics. But recall the episode of Big Bang Theory in which this conversation occurs:
Penny: [surprised that Sheldon actually might actually help her with her flower beret business] …and you know about that stuff?
Sheldon: Penny, I am a physicist. I have a working knowledge of the entire Universe and everything it contains!
Penny: [sarcastic] Who’s Radiohead?
Sheldon: [suddenly his eye begins twitching, because he’s frustrated he doesn’t know the answer] I have a working knowledge of the important things in the Universe. Good luck!
Physics tells you what may happen in the universe. It will not tell you what actually does, unless you go out and look at the boundary conditions. Anything that happens, if the universe is simply physical, must be explicable in terms of physics but what physics actually obtains is a matter of investigation. Physicists know nothing until someone finds out what the boundary conditions are, so stamp collecting is not only a valuable enterprise, it is crucial to knowledge.
So a science like biology or psychology can be autonomous to some degree. But the history of science shows that physics, and its daughter chemistry, tends to creep into all manner of domains. Much of biology now is physics and chemistry, although it goes by the names protein chemistry, molecular biology, biochemistry, and biodynamics, and so forth.
Moreover, the autonomy of these disciplines is either to be understood as ontological (there are things in these disciplines that do not have any existence in physics) or epistemic (we have to name and infer using entities of the discipline because we cannot make the inferences from physics to, say, biology). So let us take biology as the target domain, and ask: is the autonomy of biology ontological or epistemic? The question can be reframed to cover mind, society, or information technology, etc., as it suits you.
It’s pretty clear that biology is autonomous from physics to some degree, but the historical trend has been that this autonomy is not constant, but is decreasing. Historically, biology began as its own field largely because we understood so little about how, for example, organised bodies (from which the term organism derives) do things in physical terms. As we learned about things like the Krebs Cycle, cell walls and membrane structures, and the genetic code, to mention only the most widely known aspects of living systems, we began to see how living things were simply physics organised in particular ways with particular dynamics. It took us a long time, and we are not entirely free of it yet, but we learned that there is nothing “vital” about living systems that is not physical.
More and more things were reduced in biology. Sometimes they were reduced to chemical things (and no further, because the chemistry was either not understood or the details were irrelevant to the biological explanation), sometimes to physical things, and sometimes (as in the Lotka-Volterra equations of predator-prey cycles) to mathematical items and models.
Assuming that this will continue (question begging, I know, but bear with me), biology is not ontologically autonomous. If we can explain everything without remainder, there is nothing specifically biological that is not also just physics arranged in a particular way. So there is an inductive argument that reduction is correct. What weight you think this carries will depend on what value you place on inductive arguments.
So autonomy is something that can merely reflect history and our cognitive limitations, and no strong conclusions can be drawn from it.
And yet, every scientist working in sciences of complexity will affirm that there are properties that emerge in surprising ways from the underlying physical substrate. I cannot deny this on pain of being silly (this is the argumentum ab silliness, err, reductio ad absurdum). So we need to account for this if we are clubfooted reductionists* like I am.
To deal with this, I appeal to an example of John Stuart Mill’s, and a notion from information theory – surprisal value. In the next post…
*I owe this phrase to Paul Griffiths, who used it in passing. I have since adopted it as a badge of honour.
Bedau, Mark, and Paul Humphreys. 2008. Emergence: contemporary readings in philosophy and science. Cambridge, MA: MIT Press.
Clayton, Philip. 2006. Conceptual foundations of emergence theory. In The re-emergence of emergence: The emergentist hypothesis from science to religion, edited by P. Clayton and P. Davies. New York, Oxford: Oxford University Press:1-31.
El-Hani, Charbel Niño, and Alfredo M. Pereira. 2000. Higher-level descriptions: why should we preserve them. In Downward causation: Minds, bodies and matter, edited by P. B. Andersen. Aarhus: Aarhus Univ. Press:118-142.
Nagel, Ernst. 1961. The Structure of Science: Problems in the Logic of Scientific Explanation. London: Routledge and Kegan Paul.