What is holism?
Answer by Massimo Pigliucci
The term holism refers to a variety of concepts, from the idea (in medicine) that the body should be treated as a whole, rather that by focusing on its individual parts, to the rather vague concept (in New Age mysticism) that all things in the universe are somehow connected. In philosophy and the natural sciences (particularly biology), though, holism is best contrasted with reductionism, so perhaps it would be better to start with a brief analysis of the latter.
Reduction is a technique in philosophy – and by extension in the natural sciences – that was formalized by Descartes. In The Meditations, he suggested that we need to approach any given problem by the method of “divid[ing] each of the difficulties under examination into as many parts as possible, and as might be necessary for its adequate solution,” or we “reduce involved and obscure propositions step by step to those that are simpler, and then starting with the intuitive apprehension of all those that are absolutely simple, attempt to ascend to the knowledge of all others by precisely similar steps.”
The Cartesian method – of which the above is a crucial part – was adopted by other natural philosophers, such as Descartes’ contemporary, Galileo, and became an intrinsic component of the successes of physics and other natural sciences. In philosophy, the approach eventually evolved into the method of analysis used in the appropriately termed “analytical philosophy.” It allows the translation of common language sentences into logically coherent and “cleaner” versions (if you are interested, this refers to Bertrand Russell’s theory of descriptions).
There are different kinds of reductionism, only some of which may be usefully contrasted with holism. For instance, in philosophy of science one can talk about theory reduction in cases in which a higher level scientific theory (say, Mendelian genetics) can be “reduced” (i.e., reformulated) in terms of a lower-level theory (say, molecular genetics). There is no holistic counter to this type of reduction: either a theory is successfully reduced to another, or it isn’t.
More interestingly, we can distinguish between ontological and epistemic reduction, both of which can be contrasted with their holistic counterparts. Let’s consider an example to fix our ideas: imagine you meet a physicist at a cocktail party and he tells you that everything that happens in the universe reduces, at bottom, to physics. What could he mean by that? One way to interpret the claim is that the physicist is simply saying that, ultimately, everything is made of subatomic particles (or strings, or whatever the latest physics comes up with to identify the basic constituents of reality). This is certainly a reductive explanation, and it is true, as far as it goes. It also represents a case of ontological reductionism, because it says that the only things that exist are subatomic particles (or strings, or whatever). (Remember that ontology is the branch of metaphysics concerned with claims of existence.)
But now consider another possible meaning of the utterance made by our cocktail party physicist: that physics is the only relevant science because everything in the universe can be explained in physical terms. This claim is epistemological (epistemology is the branch of philosophy that deals with how we know things), and much more debatable. Even if it is true that the ontology of everything (human beings, economies, galaxies) is reducible to fundamental physics, it doesn’t follow that fundamental physics can do away with biology, psychology, economics or cosmology as independent disciplines with their own proper explanatory levels. Unless your physicist friend is ready to provide you with, say, a quantum mechanical explanation of why you two are having that particular conversation, his epistemic reductive claim fails abysmally.
Now, a holist could take issue with both the ontological and the epistemic claim, but she would probably be more successful with the latter than with the former. It is hard to imagine, given the current status of scientific knowledge, denying that everything is, in fact, made of subatomic particles (or strings, or whatever). While at the same time it is rather easy to make the case that there are many levels of complexity in the world (atoms, molecules, living organisms, ecosystems, celestial bodies), and that different types of explanations work best for distinct levels of reality: quantum mechanics isn’t going to replace economic theory, likely ever.
However, even in the ontological sense, reductionism isn’t necessarily a slam dunk. A number of philosophers have suggested that certain kinds of non material “objects,” such as mathematical structures (numbers, theorems, etc.) exist in a mind-independent, non physical fashion, and are therefore not reducible to subatomic particles (or strings, or whatever). This notion is known as mathematical Platonism, but we’ll set it aside for another time.
There is one more sense in which ontological reductionism may turn out to be problematic – and hence a holistic, or system-level, approach to be useful – though it is still somewhat speculative. I am talking about the idea of emergent properties. These are properties of complex matter that are not reducible to the properties of its simpler constituents. Take, for instance, the fact that a large enough number of molecules of water acquires the property of being wet (at certain temperatures and pressures). “Wetness” is not defined at the level of an individual molecule, or even of a small number of molecules. It only emerges when enough molecules interact together, which means that it can be studied only holistically, so to speak, not reductionistically.
Generally speaking, it is more constructive to think of the holism-reductionism contrast as a complementarity rather than an antagonism: on the one hand, we can often make progress in understanding complex systems by breaking them down into smaller chunks and see how they can be put together again; on the other hand, we still need to take seriously the idea that some things only function, or even exist, at certain levels of complexity and not below them.