Prolegomena for a Pluralist Metaphysics: Explanatory Disunity
by Daniel A. Kaufman
As readers know, I have been running a series of conversations with Crispin Sartwell, as an accompaniment to these prolegomena. I asked Crispin to do this with me for two reasons: First, he is the only person within my circle capable of addressing the many and diverse subject areas across which the prolegomena reach; and second, Crispin disagrees significantly enough with my views in these areas to provide the sort of interrogation that such complex and controversial ideas require. I am making a number of very strong claims, with regard to a number of well-entrenched – in many cases highly venerated – philosophical views, so it is critical that I receive pushback and counterargument from someone with sufficient knowledge of the relevant subject areas to do so effectively. Crispin is the first and only person I considered for the job, and I am very grateful that he has accepted it.
One important result has been that as I write these prolegomena, the course I follow is influenced significantly by Crispin’s examinations. On a number of occasions now, his objections and concerns have been motivated by a (sometimes explicitly stated) desire for explanatory unity, so I’m going to address that issue in this installment.
In the 20th century, the discussion of explanatory unity/disunity was focused on the logical positivist inspired idea of the unity of the sciences. As Jerry Fodor, an advocate of explanatory disunity described it, in his landmark paper, “Special Sciences (Or: The Disunity of Science as a Working Hypothesis”:
[Philosophers] wish to endorse the generality of physics vis a vis the special sciences: roughly, the view that all events which fall under the laws of any science are physical events and hence fall under the laws of physics. For such philosophers, saying that physics is basic science and saying that theories in the special sciences must reduce to physical theories have seemed to be two ways of saying the same thing…
What has traditionally been called ‘the unity of science’ is a much stronger, and much less plausible, thesis than the generality of physics. If this is true it is important… Reducibility to physics is taken to be a constraint upon the acceptability of theories in the special sciences, with the curious consequence that the more the special sciences succeed, the more they ought to disappear… [T]he assumption that the subject-matter of psychology is part of the subject-matter of physics is taken to imply that psychological theories must reduce to physical theories…
I wrote an entire essay on Fodor’s “Special Sciences” paper, so I’m not going to do a close reading of it here. Suffice it to say the following, in a summary capacity:
–By ‘special sciences’, Fodor intends mainly psychology and the social sciences.
–The primary explanatory mechanism of a science is its laws. (I should add that the argument need not depend on any particular account of what scientific laws are.)
–Scientific laws describe relations between a science’s kinds.
–To show that a law of one science is equivalent to another, one must show that the kinds described by that law have equivalents in the other science.
–Social scientific kinds are are only equivalent to disjunctions of physical scientific kinds, often of indefinite length.
–These disjunctions are not kinds in any science.
–The laws describing the relations between these disjunctive kinds are not laws in any science.
If social scientific laws cannot be reduced to physical laws, then social scientific explanations cannot be equivalent to physical explanations, which demonstrates that the social and physical sciences are not and cannot be explanatorily unified. Of course, laws/explanations in biology (which are teleonomic) cannot be reduced to laws/explanations in physics (which are not teleonomic) either, as my friend and biologist-turned-philosopher Massimo Pigliucci has pointed out in numerous discussions in which the subject has come up – and in one dialogue entirely devoted to the subject of teleology/teleonomy – so it would appear that explanatory disunity is ubiquitous across the sciences; that it is the rule, not the exception.
Some have tried to embrace a non-reductive physicalism that depends on the idea that psychosocial properties supervene upon physical ones. By ‘supervene’ I mean nothing beyond the standard philosophical use of the term:
A set of properties A supervenes upon another set B just in case no two things can differ with respect to A-properties without also differing with respect to their B-properties.
Supervenience is invoked to retain the idea that there is a strict “dependence” of the psychosocial on the physical, without offering any account of what the dependence consists of, which is what differentiates it from the reductionist approach. This strikes me as objectionable, in that it comes down merely to asserting a dependence relation without either justifying or explicating it. This essentially is what Stephen Schiffer (a former teacher of mine) said in his 1987 book, Remnants of Meaning:
could being told that non-natural moral properties stood in the supervenience relation to physical properties make them any more palatable? On the contrary, invoking a special primitive metaphysical relation of supervenience to explain how non-natural moral properties were related to physical properties was just to add mystery to mystery, to cover one obscurantist move with another.
There is of course the further problem that given an externalist conception of mental content (the only viable notion, as far as I am concerned, in light of the sorts of problems Wittgenstein raises with his rule-following and private language arguments, not to mention Hilary Putnam’s twin-earth thought experiment), one could duplicate a person atom by atom and that person nonetheless could be in different psychological states, since the content of those states is determined by their external relations, not just to things in the world, but to the representations, interpretations – and more broadly, the forms of life – of other people in the world. Put another way, if “meaning ain’t in the head,” as Putnam famously put it, the psychosocial will not supervene on the physical. This really should come as no surprise, in light of what I’ve already said in prior installments. Actions neither reduce to, nor supervene upon motor movements (physical events), which is why two identical sets of motor movements may constitute entirely different actions, depending on their context/interpretation, and similarly, thoughts do not supervene on neurological (physical) events, given that two entirely identical neurological events can constitute different thoughts, given their context/interpretation. Thoughts and actions are irreducibly social entities – non-hypostatically understood, of course – and are part of the space of reasons and ends which means that they belong entirely to the Manifest Image.
So much effort has gone into exploring the ways in which explanatory unity might be realized that few have bothered to ask why it even should be considered a reasonable goal. And those like Fodor who have opposed the idea of explanatory unity, have proceeded primarily from the angle of its not being achievable, rather than its being an unreasonable/undesirable goal to begin with.
That there is just one world would not seem any kind of reason for thinking that everything we know about it should ultimately cohere, as part of one account. Certainly, the fact that there is but a single world implies that the things we know about it cannot be mutually contradictory; that is, they must be consistent with one another. But the desire for explanatory unity is not simply the desire that the various things we know about the world should not contradict one another – that what we know, say, about legislation and law in democracies should be consistent with what we know about the characteristics of elementary particles – but rather that all the things we know should cohere, by which is meant not merely that A and B are consistent, but that they are mutually supporting and reinforcing. I see no reason for thinking this is true, nor even for thinking it particularly desirable.
Of course, I have said that the Manifest and Scientific Images are complementary, in that taken together, they give us a complete and single picture of the world (a use of the term that I know Mark English does not like). The manner in which they do so is in the manner of a stereoscope, but this does not require or even suggest that the two images cohere with one another or that they should be taken as part of a single explanatory framework. That there is a single picture as a result of this combination no more requires or entails explanatory unity than does the fact that there is just one world.
I don’t want to speculate as to Crispin’s reasons for wanting explanatory unity so badly, but I do wonder whether it is essentially part of a religious outlook or sensibility, as I know that Crispin is much more inclined towards religious thinking than I am. I plan to bring this up with him in the next conversation.