Arguments against the “metaphysical”/”conceptual” distinction, and replies

1. “Occamist”:An appeal to parsimony.“The phenomena of the necessary a posteriori, and of essential properties, can be explained in terms of one unitary notion of a set of possible worlds” (Jackson, FMTE, p. 70).The main phenomenon that Jackson is concerned to explain is disconcertingly specific:“...how a sentence can be necessarily true and understood by someone, and yet the fact of its necessity be obscure to that person” (p. 71). He gives a predictable and (if we again let pass the issue of the stable set of reference-fixers) not implausible 2-D-style explanation.He concludes, 

And the important point for us is that this story about the necessary a posteriori does not require acknowledging two sorts of necessity.The story was all in terms of the one set of possible worlds.” 

(Cf. Chalmers, “M&MM,” p. 14.)

Reply:The quoted remark is perfectly true, but unresponsive.First, that the “metaphysical”/”conceptual” distinction is not required to explain the specific phenomenon of how a sentence can be both necessary and a posteriori does not show that it is not required for any explanatory purpose.Second and more importantly, the distinction is not (or not primarily) an explanatory posit in the first place.As before, conceptual possibility outruns metaphysical possibility because, just as a proposition may be (semantically) entailed by the laws of nature without being true in all metaphysically possible worlds, a proposition may be entailed by some fact or law of metaphysics without being a conceptual truth: “All water is H2O,” “Nothing is both red all over and green all over,” and “Mark Twain is Samuel Clemens,” for example.If we think of possible worlds as sets of propositions, the merely conceptually possible worlds contain propositions that no metaphysically possible world contains.–Those are (broadly) logical facts, not hypotheses invoked to explain anything in particular.All the distinctions between grades of necessity and possibility??nomic vs. legal vs. biological vs. moral etc. etc.??remain in place just as before; why should metaphysical vs. conceptual be any different? 

2.

The key point is that the right way to describe a counterfactual world sometimes depends in part on how the actual world is, and not solely on how the counterfactual world is in itself.The point is not one about the space of possible worlds in some newly recognized sense of ‘possible’, but instead one about the role of the actual world in determining the correct way to describe certain counterfactual possible worlds.”(ibid., pp. 77-78).

Reply:Let us again suspend my usual reservations about the 2-D way of putting it.My problem with this second argument is that I do not see how it gets from premise to conclusion.Suppose Jackson’s “key point,” expressed in the first sentence of the foregoing quotation, is correct.How is it supposed to follow that there is no difference between metaphysical and conceptual possibility?

Perhaps this is another appeal to parsimony: we can construe the arguments of Kripke and Putnam in the two-dimensional way, so there is no need to posit a special realm of conceptual-but-not-metaphysical possibilities.But if that is the right interpretation, I would (obviously) make the same reply as I did to the first argument.The realm is not a special realm, and certainly not “some newly recognized” one; it is an already recognized sector of logical space like any other sector.But if the argument is not another appeal to parsimony, then I do not know what it is.

3.Chalmers complains that the conceptual/metaphysical distinction is arbitrary.“It may be reasonable to countenance brute, inexplicable facts about our world, but the existence of such facts about the space of possible worlds would be quite bizarre” (CM, p. 137).

Reply:If there are natures and essences, and they generate the laws of metaphysics, then the conceptual/metaphysical distinction is not arbitrary, nor are the distinctions brute and inexplicable, even if the natures and essences themselves are brute and inexplicable.Of course a modal skeptic may turn anti-realist about natures and essences, but Chalmers himself does not show any such inclination.

4.“[I]f some worlds are logically possible but metaphysically impossible, it seems that we could never know it.By assumption the information is not available a priori, and a posteriori information only tells us about our world” (ibid., italics original). 

I am not quite sure how this argument goes.Does Chalmers mean “the information” that some worlds are logically possible but metaphysically impossible?Or, more generally, that some particular proposition is logically possible but metaphysically impossible?But I think the answer is the same for each case:Modal epistemology is everyone’s problem.While I do not find it at all obvious that a posteriori information tells us nothing modal, I have no better worked out modal epistemology than anyone else’s.Obviously I do not buy Chalmers’ hyper-rationalist view that all modal knowledge is conceptual at bottom, if only because in my Quinean way I hold that purely conceptual knowledge is rare to nonexistent.(As before, some people would maintain that these deep epistemological failings should push us into or at least toward modal anti-realism, but I do not believe in letting metaphysics be driven by epistemology either.)

5.Stalnaker:“[t]o what do the metaphysical laws owe their exalted status?How are they different from mere physical laws?” (Ways a World Might Be, p. 203)

Reply:Again, it is natures and essences to which the metaphysical laws owe their exalted status.

6.“[I]t…seems that this way of drawing a distinction between conceptual and metaphysical necessity is committed to the view that mere metaphysical necessities are not really necessary.To evoke the theological metaphor, couldn’t God have created any world that is logically or conceptually possible?” (ibid., italics original).

Reply:This is a rubber arrow:Are nomic necessities not really necessary, just because there are higher grades of necessity?If not, that is only in the sense that there are higher grades of necessity; so to make Stalnaker’s objection is just to beg the question by in effect putting it to us that there is no higher grade of necessity.As for God, theologians have argued for centuries over the question of which necessities an omnipotent God would be able to alter.Some hold that He is responsible for the laws of logic themselves.

7.“[T]he real problem with this [traditional] way of thinking…is that it confuses a property of the propositions that are the contents of our speech and thought with a property of the linguistic and mental representations that have those contents” (ibid.).Metaphysical possibilities exist, or not, independently of our concepts and abilities to conceive.“It is not just that the metaphysical laws rule out the possibility that gold be something other than an element with atomic number 79—it is that if we think carefully (in light of empirical facts) about what it would be for there to be gold that was not such an element, we see that there is no such possibility for any laws to rule out” (ibid.).

Reply:For the case of natural-kind terms, Jackson, Chalmers and Stalnaker may be right; perhaps we might just as well say that to talk of a world in which gold has a different atomic number or in which water is XYZ is to misdescribe a metaphysically possible world, as that it is to describe a metaphysically impossible but conceptually possible world.(Yet notice that one would then have to specify what sort of possible world was being misdescribed and how.This is nontrivial.)But natural kinds are not the only phenomenon that motivates a distinction between conceptual necessity and merely metaphysical necessity.Singular identities are another, though Stalnaker may say that, similarly, a “world” in which Mark Twain is not Samuel L. Clemens is no world but only the shadow of a misdescribed, genuinely possible world in which someone other than Clemens writes the books published under the name “Twain.”More:“Distinct physical objects cannot occupy the same region of space at the same time.”“Abstract entities do not have causal powers.”These are not logical truths, nor are they analytic.And there are the arithmetical truths, assuming that Gödel’s Theorem prevents us from supposing that such truths are analytic.

But now, here’s a much better argument, that’s worth considering:

Jackson reminds us that the alethic modalities are not primarily features of sentences.He says that what we should be talking about is possibilities themselves and how many kinds of them there are.Presumably they are propositions or states of affairs.

Now, we Kripkean-Putnamian believers in a posteriori necessities hold our belief primarily because of a posteriori identities and the Marcus-Kripke point that genuine identities (identities whose terms are rigid designators) are necessary.But someone might argue that any two true identity sentences whose terms are rigid designators of the same individual express the same proposition.“Mark Twain = Samuel Clemens” expresses just the same singular proposition as does “Samuel Clemens = Samuel Clemens,” viz., the proposition that that person is that person.“Water = H2O” expresses just the same proposition as do “Water = water” and “H2O = H2O,” viz., that that stuff is that stuff.Moreover and more generally, outside intensional contexts coreferring rigid designators may be substituted in sentences salva propositione, so “Some water is not H2O” expresses the same proposition as “Some water is not water” and “Some H2O is not H2O.”So if we are individuating worlds according to sets of propositions, there is (at least as yet) no proposition that holds in a conceptually possible world but not in any metaphysically possible world.In particular, the proposition that some water is not H2O does not hold in a conceptually possible world, because it is one and the same as the proposition that some H2O is not H2O.So too for the proposition that Twain is taller than Clemens, which is just the proposition that Clemens is taller than Clemens.

The foregoing argument may seem to break down when it comes to natural-kind terms.For no one thinks that “water” and “H2O” are synonymous.Though hated, it is a given of the Kripke-Putnam literature that “water” and “H2O” differ in meaning.Since “water” and “H2O” do differ in meaning, “Some water is not H2O” expresses a different proposition from that expressed by “Some water is not water,” and ditto for “Some H2O is not H2O.”So, continues the objection, there is after all a proposition, expressed by “Some water is not H2O,” that holds in a conceptually possible world but in no metaphysically possible one, and the argument fails.But Jackson has a reply available.He may remind us that “water” and “H2O” do have the same “C-“ or “secondary” intension.Their difference in meaning is a difference in “A-“ or “primary” intension.The A-intension of “Some water is not H2O” is a metaphysical possibility, not a metaphysical impossibility.So there is no single intension or proposition that is metaphysically impossible but conceptually possible. 

Given the two-dimensional framework and the assumption that there are A-intensions, the foregoing seems (otherwise) to be a sound argument.Yet it could not settle the issue, because as before, there are unrelated types of sentence that do express propositions that are conceptually possible though metaphysically impossible: