Reductionism does not have quite the same hold in philosophy of science that it once did, having been subjected to powerful attack not only from Cartwright, but from (I discuss the anti-reductionist literature in detail in .) Still, the idea that whatever is real is somehow ultimately nothing more than what can in principle be described in the language of a completed physics exerts a powerful hold on many. Cartwright cites as adherents of this view, and is another prominent advocate. As Cartwright notes, in contemporary writing about science, the lure of reductionism is especially evident in discussions of the purported implications of neuroscience for topics like free will., , and many others.
Cartwright sets the stage for her discussion by quoting a famous passage from physicist Sir Arthur Eddington’s book :
I have settled down to the task of writing these lectures and have drawn up my chairs to my two tables. Two tables! Yes; there are duplicates of every object about me – two tables, two chairs, two pens…
One of them has been familiar to me from earliest years. It is a commonplace object of that environment which I call the world. How shall I describe it? It has extension; it is comparatively permanent; it is coloured; above all it is substantial… [I]f you are a plain commonsense man, not too much worried with scientific scruples, you will be confident that you understand the nature of an ordinary table…
Table No. 2 is my scientific table… It does not belong to the world previously mentioned – that world which spontaneously appears around me when I open my eyes... My scientific table is mostly emptiness. Sparsely scattered in that emptiness are numerous electric charges rushing about with great speed; but their combined bulk amounts to less than a billionth of the bulk of the table itself…
There is nothing substantial about my second table. It is nearly all empty space – space pervaded, it is true, by fields of force, but these are assigned to the category of “influences”, not of “things”. (pp. xi-xiii)
Now, reductionism holds that in some sense the first table is really “nothing but” the second table – or even that the first table does not, strictly speaking, really exist at all, and that only the second table does (though philosophers typically characterize the latter sort of view as eliminativist rather than reductionist).
The first consideration Cartwright raises to illustrate how problematic reductionism is concerns the way reductionists have, over the last few decades, repeatedly had to qualify their claims. The ambitions of reductionism have, you might say, been greatly reduced. Bold type-type reductionism gave way first to a weaker token-token reductionism, and then to yet weaker supervenience theories.
Type-type reductionist theories hold that each type of feature described at some higher-level science can be identified with some type of feature described at a lower-level science, and ultimately at the level of physics. Perhaps the best-known theory of this kind is the original mind-brain identity theory, which holds that every type of psychological state (the belief that it is raining, the belief that it is sunny, the desire for a cheeseburger, the fear that the stock market will crash, etc.) can be identified with some specific type of brain process. A stock example from the physical sciences would be the claim that temperature is identical to mean kinetic energy.
As Cartwright notes, one problem with this sort of view is that it is difficult to find plausible cases of successful type-type reductions beyond such stock examples. Another is that the stock examples themselves are not in fact unproblematic. “Reduction” claims seem really to be eliminativist claims after all. For example, given the so-called reduction of temperature, it’s not that what we’ve always understood to be temperature is really just mean kinetic energy. It’s that what we’ve always understood to be temperature is not real after all (or exists only as a quale of our experience of the physical world, rather than something there in the physical world itself) and all that really exists is mean kinetic energy instead.
A problem with supposing otherwise is that the laws that govern the features of some higher-level description and the laws that govern the features of some allegedly corresponding lower-level description can yield conflicting predictions. One way to think about this – though not Cartwright’s own example – is in terms of that descriptions at the psychological level are not law-governed in the way that the materialist supposes that descriptions at the neurological level are. Hence, even if a brain event of a certain type is strictly predictable, the corresponding mental event will not be. Given this sort of mismatch, there is pressure on the type-type reductionist to treat the higher-level description as not strictly true.
An especially influential consideration that led philosophers to abandon type-type reductionism is the “multiple realizability” problem – the fact that higher-level features can be “realized in” more than one type of lower-level feature, so that there is no smooth mapping of higher-level types on to lower-level types of the kind an ambitious reductionist project aims for. In the case of the mind-brain identity theory, the problem is that the same mental state (believing that it is raining, say) could plausibly be associated with different types of brain process in different people, or even in the same person at different times. Or consider how an economic property like being one dollar can be realized in paper currency, in metal currency, or as an electronic record of one’s bank account balance.
This led philosophers to embrace less ambitious token-token reductionist theories. The idea here is that even if types of feature at a higher level cannot be smoothly correlated with types of feature at a lower level, nevertheless every token or individual instance of a feature at the higher level can be identified with some token or individual instance of a lower-level feature. For example, this particular instance of believing that it’s raining is identical with that particular instance of a certain type of brain process.
As Cartwright notes, however, token reductions in fact tend to yield, after all, type reduction claims of a sort. An example would involve disjunctive types at the lower level of description. For instance, a token reductionist view of mind-brain relations may entail that a type of mental state like believing that it is raining is identical to a “type” of neural property defined as being in brain state of type B1 OR being in brain state of type B2 OR being in brain state of type B3 OR… And this will, in turn, open up the possibility of a conflict between what the laws that govern the higher-level description entail and what the laws that govern the lower-level description entail.
If it is objected that disjunctive “types” of the kind just described seem artificial, that is certainly plausible. But the problem, as Cartwright notes, is that this illustrates how identifying what counts as a plausible type is going to require detailed metaphysical analysis, and cannot be read off the science, as the reductionist supposes.
In any event, token-token reductionism gave way in turn to talk of supervenience. The basic idea here is that phenomena at some higher level of description A supervene on phenomena at some lower level of description B just in case there could not be any difference at what happens at level A without some corresponding difference in what happens at level B.
But exactly what this amounts to is not obvious, and debating the meaning of supervenience has, Cartwright complains, been a bigger concern of philosophers than explaining exactly why anyone should believe in it in the first place. (More on this in a moment.) As its vagueness indicates, supervenience entails an even weaker claim than token-token reduction. Though, in recent years, there has been a lot of heavy going about “grounding,” which, Cartwright notes, is stronger than supervenience. The idea is that all facts are “grounded” in the facts described at the level of physics, in the sense that whatever happens at the higher levels is “due to” what happens at the lower, physics level. But here too, why suppose this is the case?
Where the claim that everything supervenes on the level described by physics is concerned, Cartwright says, there are three basic reasons given for it, none of them well worked out or convincing. First, there is a leap from the fact that the lower-level features described by physics affect what happens at the higher levels, to the conclusion that those features by themselves entirely fix what happens at the higher levels. This is simply a non sequitur.
Second, there is a leap from the supposition that successful reductions have been carried out in a handful of cases, to the conclusion that reductionism is in general true. But this too is a non sequitur (and on top of that, the premise is questionable). Third, there is the claim that physicalistic reductionism is in fact the method applied within science. But this, Cartwright argues, is simply not true to the facts of actual scientific practice.
“Grounding” accounts of reduction suppose that the level described by physics is the sole cause of what happens at the higher levels, and also that it is in no way itself caused by what happens at the higher levels. These claims too, argues Cartwright, are not supported by actual scientific practice.
Here she appeals in part to recent work in the philosophy of chemistry, in which two general lines of anti-reductionist argument have been developed. The first and more ambitious of them argues that chemistry as a discipline rests on classificatory and methodological assumptions that are simply sui generis and make the features of the world it uncovers irreducible to those uncovered by physics. The second does not rule out reductions a priori, but argues on a case by case basis that purported reductions have not in fact successfully been carried out. (I discuss this work in philosophy of chemistry at pp. 330-40 of Aristotle’s Revenge.)
But it is not just that chemistry and other higher-level sciences are not in fact “all physics” at the end of the day. As Cartwright emphasizes, “even physics isn’t all physics.” For one thing, “physics” covers a range of branches, theories, and practices, not all of which have been reduced to the most fundamental theories. For another, even the fundamental theories themselves are not fully compatible with each other, the notorious inconsistency between quantum mechanics and the general theory of relativity being a longstanding and still unresolved problem. She adds:
The third and to me most important point is that in real science about real systems in the real world, for predictions and explanations of even the purest of physics results, physics must work in cooperation with a motley assembly of other knowledge, from other sciences, engineering, economics, and practical life. (p. 110)
Cartwright then goes on to describe in detail the Stanford Gravity Probe B project as an illustration of the vast quantity of theoretical knowledge and practical know-how that are necessary in order to apply and test abstract physical theory, yet cannot itself be reduced to such theory. This recapitulates a longtime theme in Cartwright’s work over the decades, viz. that the mathematical models and laws of physics are idealized and simplified abstractions from concrete physical reality, and do not themselves constitute or capture concrete physical reality.
In short, reductionism, Cartwright judges, is poorly defined and poorly argued for. Its lingering prestige is unearned.
I’ve mainly just summarized Cartwright’s arguments here, since I sympathize with them and they supplement those that I develop in Aristotle’s Revenge. They give us, though, only her case against the views she opposes, rather than the positive account she’d put in place of them, which is described later in the book. More on that in a later post.