Fine's Harmless Modal Pluralism
In "The Varieties of Necessity", Kit Fine defends Modal Pluralism. Does he thereby threaten Modal Realism? He says he does (in footnote 5). But does he really?
Well, what is Fine's thesis of Modal Pluralism? Here is his summary:
I conclude that there are three distinct sources of necessity -- the identity of things, the natural order, and the normative order -- and that each gives rise to its own peculiar form of necessity. Neither form of necessity can be subsumed, defined, or otherwise understood by reference to any other form of necessity. (p.279 of Conceivability and Possibility)
It seems that he is mixing several different theses here. In particular,
- There are three distinct sources of necessity; i.e. distinct explanations of why a statement has the modal status it has.
- Three distinct notions of necessity have to be taken as primitive, because neither can be analysed away in virtue of the others, nor in virtue of anything else.
- There are three distinct classes of necessities, neither of which is a subclass of any other.
(3) can be ruled out immediately. Fine offers no reason at all to believe that e.g. some natural possibilities are metaphysically impossible. When he says that none of the three necessities can be "subsumed" under any other, he means that they can't be defined in a certain way by means of the others; which is claim (2).
The bulk of Fine's paper appears to be concerned with (2). But (as Christian Nimtz pointed out to me) it seems that (1) is Fine's real point. Consider his rejection of attempting to define natural necessities as truths entailed by the laws of nature: "[this] does not provide an adequate account of the natural necessity of the 'laws' themselves" (p.265). He asks for an explanation of what gives, say, 'F=ma' its modal status; to which the answer can hardly be that it is entailed by 'F=ma'.
The complaint is fair. 'F=ma' has modal strength, e.g. supports counterfactuals, not because it entails itself but rather because it is a law of nature. (Well, suppose it is.) What makes it a law of nature -- and thereby gives it its modal strength? Perhaps its occurrence in the best theory, or perhaps relations among universals. Something like this is the 'source' of natural necessity.
Fine also complains that "why are the laws of nature natural necessities?" must have a non-trivial answer. I disagree. The concept of natural necessity is tied to the concept of laws. I wonder what Fine's position on this matter is. It seems that he wants to take 'natural necessity' as primitive. If moreover it is not conceptually true that the laws of nature have this primitive kind of necessity, laws of nature can't be defined in terms of natural necessity. Perhaps they are defined in Mill-Ramsey-Lewis or Dretske-Tooley-Armstrong manner. But then how come the laws of nature are natural necessities? Is this a brute, inexplicable fact? Could it be different? Could the laws of nature be naturally contingent, while accidental regularities are naturally necessary? That sounds crazy. The alternative is to assume that some inexplicable metaphysical tie assures that at every world, whatever satisfies the Mill-Ramsey-Lewis or Dretske-Tooley-Armstrong criteria happens to be a natural necessity. That also sounds crazy.
So I think one should accept that if 'F=ma' is a law of nature then it is a natural necessity, and trivially so. This means that the concept of natural necessity can be reduced to other concepts. Not so much to other modal concepts, but to the concept of laws. (Though modal concepts might occur in analysing what it means to be entailed by a law.) It follows that Fine's thesis (2) is false. What's true (at least in the present case) is his thesis (1): if L is a natural necessity, the ultimate explanation for why it has that status is something like the content of best physics or the relations among universals. And this is certainly not what explains the modal status of metaphysical or normative necessities.
So understood, it is hard to imagine how anyone could reject thesis (1). Suppose (1) is false. Then whatever explains the metaphysical necessity of a statement (say, the identity of things) also explains why a statement is naturally and normatively necessary. This implies that metaphysical necessity, natural necessity and normative necessity coincide. If that is modal monism then nobody should want to be a modal monist.
It even seems to me that 3 is far too small as the number of distinct 'sources' of necessity. For instance, what makes "there are no trains faster than 10000 km/h" a technical necessity? And what gives "2+2=4" and "p or not p" and "all bachelors are unmarried" their modal strength? Certainly not 'the natural order' or 'the normative order'. So it must be 'the identity of things'. What things? It seems to me that the best explanation of why "all bachelors are unmarried" is necessary should rather involve facts about meaning, in particular the fact that "bachelor" means "unmarried man". Fine argues that these other necessities can be defined in terms of metaphysical necessity and other concepts. Right, but that answers thesis (2), and it is also true for natural and normative necessity.
What does this all mean for Modal Realism? Thesis (3) would be a problem. It would mean that the space of metaphysical possibility does not contain all possibilities; that besides the metaphysically possible worlds one must also postulate naturally and normatively possible worlds, some of which are metaphysically impossible. But thesis (3) is not Fine's thesis.
Thesis (2) would be a minor inconvenience. It would mean that Modal Realism doesn't deliver a reduction of all modal notions. The fact that it does (or promises to do) is certainly an attractive feature of Modal Realism. But it is not its main purpose. A Modal Realist could well live with the fact that some worlds are naturally possible (with respect to our world) even though this is a primitive fact about those worlds. Anyway, I've argued that thesis (2) is not Fine's thesis either. His 'Modal Pluralism' is thesis (1), which is no problem at all.