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
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
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:
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
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: