Roughly, the principle of recombination says that anything can coexist and
fail to coexist with anything else. But that's too strong: things do
have essential extrinsic properties; if Kripke's origin is essential
to Kripke, Kripke cannot fail to coexist with his ancestors. However, a
perfect intrinsic duplicate of Kripke could fail to coexist with Kripke's ancestors.
So less roughly, the principle of recombination goes somehow like this:
For any things in any possible world there is a world
which contains any number of perfect intrinsic duplicates of all those
things and nothing else (i.e. nothing distinct from all these
duplicates).
What is a perfect intrinsic duplicate? Something that has exactly
the same intrinsic properties as the original. What
is an intrinsic property? A property that belongs to objects
independently of what exists and goes on around them. The
instantiation of an intrinsic property in some region of a world is
independent of the instantiation of intrinsic properties in other
regions.
Some philosophers seem to believe that narrow content must be defined without resort to external objects, leaving only bizarre options like phenomenalism, conceptual role semantics and global descriptivism. But that's wrong. Narrow content can and should be defined by external causal relations just like wide content.
By narrow content, I mean a kind of mental content that doesn't much depend on the subject's environment. Completely narrow content is altogether
intrinsic to the subject. But hardly anyone believes in completely
narrow content. The question is whether there is an interesting kind of content shared between my intentional states and the states of my
twin on twin earth -- and those of swampman and those of a brain in a vat.
I've been working on several other websites this summer, one of which needed a blog. After struggling with Wordpress for several hours, I gave up and worked a little more on my own script instead. So here's a new version.
I believe that the so-called problems of intrinsic change and accidental intrinsic properties are real problems. But I believe that their names are misleading, and that they have nothing to do with whether or not we construe properties as sets of things or as functions from worlds and times to sets of things.
Suppose we do the latter, and we also endorse counterpart theory and temporal parts theory. The property of being bent is a function that maps world-time pairs to sets of things. These things are temporal parts of world-bound individuals, ordinary fusions of particle segments, just like us, except that they are smaller along the time axis and all bent. This is a perfectly reasonable and common-sensical view, I believe (but of course I'm biased), and I don't think Lewis has any reason to reject it as turning properties into relations. There is after all a simple equivalence between being bent construed as a function and being bent construed as a Lewisian set: the set is the union of the range of the function; the function indexes all members of the set by their world and time.
I'm updating the software behind this weblog. If everything looks broken in the next half our or so, that's the reason.
Update: OK, done. If you notice any problems, please let me know.
For many things, there is no set that contains just those things. There is no set of all sets, no set of all non-self-members, no set of all non-cats, no set of all things, no set of pairs (x,y) such that x is identical to y, no set of (x,y) with x part of y, no set of (x,y) with x member of y.
If Lewis is right and there are proper-class many possibilia, there is also no set of possible philosophers, no set of possible dragons and no set of possible red things. However, if Lewis is right and there are proper classes, there will be proper classes of all these things. But there will still not be a class of all classes, a class of all non-self-members, a class of all non-cats, etc.
This is a follow-up to yesterday's entry.
Andy Egan argues that functions from worlds and times to sets of things are ideally suited as semantic values of predicates, even better than mere sets of things.
I agree, and so would Lewis. In fact, Lewis would say that functions from worlds and times are still too simple to do the job of semantic values. There are more intensional operators in our language than temporal and modal operators. Among others, there are also spatial operators and precision operators ("strictly speaking"). So our semantic values for predicates should be functions from a
world, a time, a place, a precision standard and various other 'index coordinates' to sets of objects. This is more or less what Lewis assigns to common nouns in "General Semantics" (see in particular §III). Other predicates like "is green" that do not belong to any basic syntactic category get assigned more complicated semantic values: functions from functions from indices to things to functions from indices to truth values. In later papers, Lewis argues that we may need several of the world and time coordinates and, more
importantly, a further mapping that accounts for context-dependence
(and to deliver the kind of truth-conditions needed in his theory of
linguistic conventions). Thus for predicates, we get something like a
function from centered worlds to functions from functions from possibly several worlds, times, places, precision standards, etc. to functions from such worlds, times etc. to truth values. (Alternatively, if we go for the 'moderate external strategy' (Plurality) and reserve "semantic value" for 'simple, but variable semantic values' ("Index, Context and Content"), we can say that the semantic value of a predicate in a given context is the value of the function just mentioned for that context.)
Andy Egan, in "Second-Order Predication and the Metaphysics of
Properties", argues that there is a bug in Lewis' theory of
properties which can be fixed by identifying properties
not just with sets but with functions from worlds (and times) to
sets. I disagree: there is no bug. But there are some interesting
questions about Lewisian properties nearby.
Here's the alleged bug. Consider the second-order property being
somebody's favourite property. This property belongs to
Green. So on Lewis' account, Green is a member of the
set being somebody's favourite property. But at another
possible world, Green is nobody's favourite property. So it is not a member of that set. Contradiction. In the parallel case of accidental properties of individuals, Lewis resorts to counterpart theory: If Graham Greene is a writer in our world and not in another world, that's not because Greene both is and isn't a member of the set writer, but because Greene is a member while one of his counterparts isn't. However, this solution doesn't work for Green because properties don't have counterparts.
I would like to believe that all necessary truths fall into the following two kinds.
1. Analytic truths. By processing the semantic content of such a sentence we can find out that its truth conditions are universally satisfied, no matter how the world turns out and no matter what
other world we talk about.
2. Truths whose evaluation at other worlds depends on contingent features of the actual situation. What we can know by linguistic processing is that if these features are so as to make such a sentence true, then it remains true even when we talk about other worlds, that is, when the sentence is embedded in "at world such-and-such" or "necessarily". For example, if we know that there are sheep, we can figure out that "actually, there are sheep" is necessary, because
it is a rule of our language that (roughly) "actually p" is true at a
world w iff p is true at the actual world. Knowledge about ordinary,
contingent features of the current situation together with linguistic
competence always suffices to learn that these a posteriori necessary
sentences are true.
Some forms of descriptivism say that when I utter a sentence with a proper name in it, communication only succeeds if there is a description, a set of properties, you and I both associate with that name. But often such descriptions are hard to find, so some conclude that instead it suffices if you and I refer to the same object with that name, no matter what properties mediate our reference or if it is mediated by associated properties at all.
In fact, shared reference doesn't quite suffice for successful communication. We should also require that the shared reference is common knowledge. If I tell you that Ljubljana is pretty but you have no idea whether by "Ljubljana" I refer to the town you call "Ljubljana" or whether instead I refer to my neighbour or the moon, you don't understand what I'm trying to tell you.