I've been invited to this year's German-Italian Colloquium in Analytic Philosophy, for which I've put together some remarks on the philosophy of mathematics: "Emperors, dragons and other
mathematicalia" (PDF). I mainly argue that mathematical sentences should be interpreted as quantifications over possibilia. Technically, this isn't really new. Daniel Nolan in particular has made a very similar suggestion (PDF). What hasn't been emphasized enough, I believe, is that this interpretation not only works from a technical point of view, but is quite attractive for various philosophical reasons. (Unlike Nolan, I argue that it isn't a reform, but a faithful interpretation of mathematics.)
What can we say about physical systems when they are not in an eigenstate of a certain property? For instance, what can we say about an electron's x-spin when it is in a superposition of 'up' and 'down'?
We can say that a measurement of the property will (or rather, would) deliver such and such results with such and such probability. Most physicists apparently think that this is more or less all we can say. In particular, they argue that we should not interpret the superposition state as something like "the probability that the electron now actually has x-spin up is 0.5": having x-spin up (or down) requires being in an eigenstate of x-spin, but the electron is in no such eigenstate; thus the electron definitely has neither x-spin up nor x-spin down; it is in a superposition state, and that's all there is.
One can think of perception as a relation between states (or acts) and objects, the objects that are perceived. Alternatively, one can think of it a relation between a state and a content, the information acquired or represented in the perception.
Content is something that excludes possibilities. Suppose I have a perception of an elephant standing in front of me. What possibilities are thereby excluded? There are at least two reasonable answers: 1) the exluded possibilities are possibilities where there is no elephant in front of me; 2) the excluded possibilities are possibilities where I do not have that experience. Regarded as sets of possible situations, on the first account, the content of my perception is a set of situations in which there is an elephant in front of me. On the second, it is a set of situations where I have the phenomenal experience I actually have, even if it is caused by evil scientists. (Strictly, "I" need not be me, but can be whatever is in the center of the relevant situation.)
Suppose
1) the facts about use etc. underdetermine the semantic value of term
x (to a certain degree).
But
2) the semantic value of x is not underdetermined (to that degree).
Let V1,V2,... be the semantic values between which x is
underdetermined, and suppose V2 is in fact the value (or range of values) of x. What is it
about V2 that makes it the semantic value? Not 'use etc'. But
suppose all obvious candidates like causal facts are part of 'use etc.'. Then the
relationship between x and V2 -- let's call it "reference" -- is
inscrutable insofar as knowing all ordinary facts about use and
causation and so on is not enough to find out that
x refers to V2. There must be something over and above all this that
privileges V2. Let's say (with Lewis) that V2 is a reference
magnet (with respect to x).
Panpsychism is the view that all physical things have, besides their physical properties, also psychological or phenomenal properties. The psychological properties are commonly assumed to be intrinsic. The idea is that physics only tells us about the structural and relational properties of things, but remains silent on what it is -- intrinsically -- that has all these dispositions and stands in all these relations to other things. So if we want to attach fundamental psychological properties to electrons (for example), we may well say that they are those physically unknown intrinsic properties: electrons ultimately are pain (say). But that's not essential to what I mean by "panpsychism". If you say that all physical entities have fundamental and irreducible, but extrinsic psychological properties, that's also panpsychism.
Oh dear.
Returning to philosophy, here is a remark by John Burgess about the possibility of translating ordinary sentences into sentences with seemingly less ontological commitment, as described in Prior's "Egocentric Logic" and Quine's "Variables Explained Away":
Thus whether one speaks of abstract objects or concrete objects, of simple objects or compound objects, or indeed of any objects at all, is optional. Or at least, this is so as regards "surface grammar". My claim is that if children who grew up speaking and arguing in Monist or Nihilist or some Benthemite hybrid between one or the other of these and English, it would be gratuitous to assume that the "depth grammar" of their language would nonetheless be just like that of English, with a full range of nouns and verbs denoting a full range of sorts of objects and connoting a corresponding range of kinds of properties. And any assumption that the divine logos has a grammar more like ours and less like theirs would be equally unfounded, I submit. It is in this sense that I claim any assumption as to whether ultimate metaphysical reality "as it is in itself" contains abstract objects or concrete objects, of simple objects or compound objects, or again any objects at all, would be gratuitous and unfounded. (p.18 of "Being Explained Away" -- Microsoft Word format, use Neevia to convert)
I'm not sure to what extent I agree with that. I do agree that there is something strange about asking whether numbers really exist. Burgess takes this to be the core question dividing nominalism and platonism about numbers. Thus he argues e.g. in "Nominalism Reconsidered" (MS Word again, coauthored with Gideon Rosen) that if nominalists agree that "there are numbers" is true -- while offering a nominalistically acceptable interpretation --, they have actually given up nominalism.
Philosophers like to paraphrase away ontological or ideological commitment: how can there be a lack of wine if there are no such
entities as lacks? Because "there is a lack of wine" is only a loose way of saying "there is not enough wine".
So do we suggest that "there is not enough wine" somehow gives the
underlying logical form or linguistic structure of "there is a lack of
wine"? One might think so: if there are no lacks, we can't honestly
use lacks as semantic values in our linguistic theory. So if 1) our
linguistic theory says that sentences of the form "there is an F" are
true iff the relevant semantic value of "F" is non-empty, and if 2)
"there is a lack of wine" has the form "there is an F", and if 3) the
members of a predicate's semantic value are things that (in some
intuitive sense) satisfy the predicate, then, given the truth of "there is a lack of wine", it follows that there are things satisfying "is a lack of wine". Which presumably we wanted to deny. Rejecting (2) seems to be a good way to block the argument: "there is a lack of wine" is
not really a sentence of the form "there is an F"; really, it
is a sentence of the form "there is not enough G".
Stalnaker's "Lewis on Intentionality" (AJP 82, 2004) is a very odd paper. The aim of the paper is to show that Lewis's account of intentional content as developed in "Putnam's Paradox" -- global discriptivism with naturalness constraints -- faces various problems and conficts with what Lewis says elsewhere.
The first thing that's odd about this is that in "Putnam's Paradox", Lewis doesn't develop an account of intentional content. Rather, he discusses Putnam's model-theoretic argument and suggests that if one holds something like global descriptivism about linguistic content, adding external naturalness constraints on the interpretation of predicates would be an attractive way to block Putnam's argument for underdetermination.
Sometimes I think it's unfortunate that advanced logic and metamathematics usually presuppose various mathematical truths. For instance, in discussions on mathematical realism I've heard people arguing that by the first incompleteness theorem, mathematical truth can't be identified with provability in a formal deductive system. For, those people argue, the first incompleteness theorem proves that for any reasonable formalized system of mathematics, there is a true arithmetical sentence G that is unprovable in the system.
I've written a little paper in German about the connections between metaphysical (modal) and analytical implication for the Olaf Müller-Kolloquium here at Humboldt University: "Fundamentale Wahrheiten" (PDF). It brings together some things I've already written about here. The main ideas are entirely due to Lewis, Jackson and Chalmers.
Since I haven't slept last night and feel unable to do anything productive, here is an abbreviated translation.