This is the Fourth Part of a review of Science Unlimited? The Challenges of Scientism, edited by Maarten Boudry and Massimo Pigliucci. See also Part 1: Pseudoscience, Part 2: The Humanities, and Part 3: Philosophy.
Reductionism is a big, bad, bogey word, usually uttered by those accusing others of holding naive and simplistic notions. The dominant opinion among philosophers is that reductionism does not work, whereas scientists use reductionist methods all the time and see nothing wrong with doing so.
That paradox is resolved by realising that “reductionism” means very different things to different people. To scientists it is an ontological thesis. It says that if one exactly replicates all the low-level ontology of a complex system, then all of the high-level behaviour would be entailed. Thus there cannot be a difference in high-level behaviour without there being a low-level difference (if someone is thinking “I fancy coffee” instead of “I fancy tea”, then there must be a difference in patterns of electrical signals swirling around their neurons).
To philosophers, however, “reductionism” is about explanations and theories. It asserts something along the lines that high-level explanations can always be translated into low-level explanations, and that the low-level explanations are more important or more proper, and that ideally the high-level explanations could be dispensed with. I say “something along the lines” because this sort of eliminative reductionism is pretty much a strawman in that no-one (sensible) advocates it. And philosophers are right, in general it does not work.
But the scientific notion of ontological reductionism does work. At least, all of science assumes that thesis, and science works very well, producing unarguable and unmatched mastery of technology and engineering. Since adopting that thesis works so well we can be pretty sure that ontological reductionism (which philosophers may instead refer to as “supervenience physicalism”) is a true feature of the real world.
But the different meanings lead to miscommunication. “Scientism” is supposed to include a naive faith in reductionism, which the accuser would take to be the philosophers’ inter-theoretic reductionism. But those defending scientism are likely to think like scientists, and so hold only to ontological reductionism but not defend ideas of inter-theoretic reductionism. The latter might work in limited instances, but does not work in general.
Most physicists would agree. In his Reductionism Redux essay, Stephen Weinberg refers to inter-theoretic reductionism as “petty” reductionism, saying that it usually doesn’t work, while he regards ontological reductionism as a “grand” reductionism that underpins all of science. Similarly Sean Carroll defines reductionism as the idea that “objects are completely defined by the states of their components”, and says: “I could imagine hypothetical worlds in which reductionism failed … It’s just not our world”.
Carroll also says that one can “object to the claim that ‘the best way to understand complex systems is to analyze their component parts, ignoring higher-level structures’, but only if you can find someone who actually makes that claim”, and adds that: “nobody thinks that the right approach is to break a giraffe down to quarks and leptons and start cranking out the Feynman diagrams”.
So let’s see what the philosophers in Boudry and Pigliucci’s book make of the concept. Filip Buekens accepts Alex Rosenberg’s claim that “physics fixes all the facts” (by which Rosenberg means the supervenience thesis that the state of a complex system is completely specified if all its low-level physical properties are specified), but he demurs about the “much stronger claim” that “all other facts are ultimately explained by physics”.
He continues: “conceptual anti-reductionism holds that explanations employing psychological concepts cannot be replaced by explanatory strategies relying on physical concepts”. So one could not translate the concept “fear” into language about electrons and protons and their motions.
He’s right on the latter point, but it’s important to realise that explanations are not mutually exclusive. Explanations are always commentaries about some aspect of a system. They never describe the entirety of a system. And that means that multiple different explanations can be true at the same time.
The doctrine of supervenience says that one could — given an advanced Star Trek transporter device — exactly replicate a system from an exhaustive listing of every particle it contains (and the replicated system would manifest the same high-level properties including “fear”). But an “explanation”, being a commentary about aspects of a system, never contains enough information to do this. You could not feed “Tom was afraid of the dog” into the transporter and exactly replicate Tom and the dog from that alone.
The same holds for explanations used in physics. They also are reduced-information commentaries; physicists no more work with exhaustive listings of particles than psychologists do — they are too unwieldly and so impractical as to be useless. Thus, even in physics there are multiple higher-level concepts (such as “temperature”, “entropy”, “elasticity”, “ductility”, “conductivity”) that are properties of an ensemble, and which are not even defined at the lower level of single particles.
Since, for any system, there will always be many mutually-consistent and equally-true explanations, it follows that even if one develops explanations of high-level properties in terms of lower-level properties, these will never replace and do-away with high-level explanations, they will only add to and complement them.
Richard Feynman said that any good theoretical physicist knows six different ways of thinking about the same thing. Explanations at different levels of description are complementary ways of thinking about the same thing. They don’t replace or abolish other explanations, instead they must all be simultaneously true. And the different explanations are held together, coherently, not by the philosophers’ notion of inter-theoretical reductionism — not by translations between different explanations — but by the doctrine of ontological reductionism or supervenience.
As an aside here, philosophers use the weird term “special science” for sciences where inter-theoretic reductionism is held not to work, and by doing that they imply that it does work for at least some sciences, by which they usually mean physics or perhaps fundamental physics; they are wrong, it does not work even there, there are no “special” sciences since they are all “special”.
I can’t help thinking that much philosophical travail against inter-theoretic reductionism is misplaced, in the sense of attacking doctrines that no-one holds. Stephen Pinker’s essay on the humanities aroused fears of a hostile take over that reduces the humanities to a mere adjunct of science. But, as Russell Blackford explains in his contribution to the volume, that is a mis-reading of Pinker, who is instead arguing for a consilience in which different styles of approach complement each other.
Similarly, Taner Edis expounds a scientism that “highlights continuities in the various ways we produce knowledge, and weaves the products of our knowledge-seeking enterprises into a naturalistic overall picture”, saying that: “this scientism is harmless: it seeks connections and coherence, not intellectual conquest”.
The most direct condemnation of reductionism in the book is by Mariam Thalos. Declaring reductionism “the enemy”, she argues against sociobiology and the claim that, because human brains have evolved “therefore biology explains human behaviour too, utilizing principles of natural selection”. But that’s true, it does!
Thalos, however, suggests that accepting this idea “would with one stroke sweep away all competing models of human behaviour”. Interpreting that narrowly, yes it would sweep away competing models — those that are incompatible with the sociobiology perspective. But it would not sweep away complementary models and explanations — those that are different from but compatible with the evolutionary perspective, and which are equally true.
Thalos generalises her argument: physics explains the behaviour of physical bodies, humans are made of physical stuff, therefore physics explains human behaviour. “Whence, biology, as such, is made irrelevant.”
To this she adds that if we accept that “physics explains human behaviour, utilizing physical principles”, then “we are explicitly denying the need for biological theory as independently valuable in the enterprise of scientific explanation”. Thus, to Thalos, only one type of explanation can be valid. Physical systems can only be explained in physical terms; biological systems can only be explained in biological terms.
No! This is a rejection of the “grand reductionism” that is the very soul of science. Complex systems (such as humans) need explanations at all levels of analysis. We should develop explanations of humans in physical terms, and in chemical terms, and in bio-chemical terms, and in biological terms, and in evolutionary terms, and in psychological terms, and in sociological terms, and in the languages of the humanities. All such explanations complement each other and mesh into a grand, consilient picture. The different explanations don’t compete with or displace each other, they complement each other. They must all be mutually compatible and mutually build to an overall grand picture in which they are all true.
That follows from the doctrine of scientific or ontological reductionism, which holds everything together because it tells us that all these different explanations are about the same ontological stuff; they are reporting different aspects of the same ensemble. And that is the consilient grand picture of science and of scientism.
This is not a merely philosophical point, it is eminently practical. Given multiple explanations about the same stuff, we then need to ensure that they are fully compatibile, and investigating that is the central driving force of science. Ensuring that the explanations in physical terms mesh seamlessly with the explanations in chemical terms, and with the bio-chemical explanations, the biological explanations, and the evolutionary and psychological explanations, is exactly how science makes progress.
Any field that wants to stand aside from that process risks turning itself into a parochial fiefdom prey to fads and ideologies (a current example being areas of sociology that totally ignore the genetic underpinnings of human behaviour), and deprives itself of the best tool that science has.