Is Talk of 'Possible Worlds' Wholly Dispensable?

I made a bold claim earlier:

If I am right, the patois of possible worlds is a dispensable manner of speaking: we can make every [modal] point we want to make without engaging in possible worlds talk.  What I just said is not perfectly obvious and there may be counterexamples. 

Here is a candidate counterexample that I borrow from Barbara Vetter, 'Can' Without Possible Worlds, 22:

(CC) Someone can see us.

This is an alethically or as Vetter would say "dynamically" modal statement. It is modal but not expressive of either epistemic or deontic modality. Interestingly, (CC) is susceptible of being read either de re or de dicto:

(DR) There is a person who can see us.

(DD) It is possible that someone see us.

(DR) commits us to an actual person who is able to see us.  (DD) does not. The first entails the second, but the second does not entail the first. So the two readings are non-equivalent.  Suppose that no actual person can see us. Suppose, that is, that no actual person has both the ability to see us and is positioned in such a way that he can exercise his ability. Even so, it is  'surely' possible that there be such a person. There could have been a person, distinct from every actual person, who sees us. 

So (DD) is a true alethically modal statement whose truth is not grounded in, or made true by, a power or ability of any actual item.

(DD) would thus appear to be a counterexample to Vetter's "potentiality semantics" according to which "all dynamic modality is de re . . . ." (22)  It seems that (DD) expresses a 'free-floating' possibility, one not grounded in any actual concrete thing's power or potentiality. If so, then 'possible worlds' talk might not be wholly dispensable.  

One response to the putative counterexample is rejectionist: Vetter toys with  simply rejecting (DD) as a statement of dynamic modality by suggesting that it is really an example of epistemic possibility (23).

I fail to see, however, how (DD) could be construed as epistemic.  The idea is not that, for all we know, someone can see us, but that it is really possible, apart from our knowledge and ignorance, that there be someone who can see us.  In the actual world, no one can see us now. But 'surely' there is a possible world, very much like the actual world, in which someone can see us now.  If there is this possibility, it is real, not epistemic. 

But there is another line of rejection that Vetter does not clearly distinguish from the first.  And that is simply to say that her topic is dynamic modality, the sort of real modality that we encounter in actual changing things, and not real modality in general.   'Dynamic' is from the Greek dynamis which in Latin is potentia, whence our 'potency' and 'potentiality.' The second way of rejection, then, is to dismiss (DD) as simply off-topic.

But then her thesis is less interesting: it is not the thesis that all alethic modality is de re, but that only the modality of actual concrete things subject to change is de re.  If this is her thesis, then it seems we need possible worlds to accommodate such de dicto possibilities as (DD). 

Comments

[Frank]

Thank you for devoting so much time to answering my question.
I admit I am still surprised that philosophers smarter than I am find this apparatus clarifying, but at least I am clearer on one point: if you are correct, PW talk is philosophically neutral--which is not always the case when, e.g., someone wants an extensional account of something.
Having said that, I now see another thing I don't understand. If PW talk is just another way of saying the same thing, it must be possible--mustn't it?--to explain Lewis' position ("actual" is indexical), his reasons for it, and others' objections to it, without such talk, but it is not obvious to me how to do so.

[BV]

I get the impression you are confusing PW talk with the ontology of PWs.

There are possible worlds in which I stayed in engineering and didn't go into philosophy. But I could say the same thing without using PW jargon: I might have stayed in engineering and not have gone into philosophy.

I don't have to worry about what possible worlds ARE. And I certainly don't have to adopt the concretist scheme of David Lewis.

I can talk the talk without walking the Lewisian walk.

[Frank]

I was not assuming that one has to accept Lewis' position, or even have an opinion about it. My idea was that if PW talk is dispensable, then every statement in the PW literature can be translated back into language that makes no mention of PWs. But I don't see how you can explain what Lewis' position is, or the pros and cons of it, without such reference. And if you can't, doesn't that imply that the PWers are adding something substantive? I've been trying to think of an analogy; it doesn't seem to be on a par with expressing "Every boy loves some girl" in logical notation.

I admit that I'm not sure that this is a good question; maybe I'm not seeing something obvious. But I don't think I 'm making the mistake you attribute to me.

[BV]

You are right that one cannot explain what Lewis' position is without PW talk. >>And if you can't, doesn't that imply that the PWers are adding something substantive?<<

No. And why do you conclude that? It is not clear what you mean by "adding something substantive"?

The question is whether we can express modal truths without invoking the apparatus of possible worlds.

Example. I am not now playing the guitar, but I can play the guitar. There is no need to invoke merely possible worlds in which I am now playing the guitar; it suffices to say that I have the presently unexercised ability to play the guitar.

The truthmaker of 'I can play the guitar' is not what some Lewisian counterpart of me is doing in some possible world, but the ability (power, capacity) I possess to play the guitar.

But then what do we do with (DD) above?