Problems with possible worlds modalism.

[Dominus Paradoxum]

‘Necessary’ cannot be construed as ‘obtains in all possible worlds’, for why does it obtain in all possible worlds? Presumably, because it necessarily obtains, but in possible worlds modalism this can only mean that it obtains in all possible worlds because it obtains in all possible worlds, which is a tautology and thus not an explanation. Obtainment in all possible worlds, then, gives us one consequence of necessity, but not a definition of it. Also, why is it, for example, that square circles do not exist in any possible world? Presumably, because they are impossible. But in possible worlds modalism, this can only mean that they exist in no possible word because they exist in no possible world, which seems rather arbitrary. The very point at issue is why they don’t exist in any possible world. Also, according to modal realism all possible worlds necessarily exist. But, according to modal realism, this can only mean that all possible worlds exist in all possible worlds, which is nonsense.

[Clutch]

Originally posted by Dominus Paradoxum
‘Necessary’ cannot be construed as ‘obtains in all possible worlds’, for why does it obtain in all possible worlds? Presumably, because it necessarily obtains, but in possible worlds modalism this can only mean that it obtains in all possible worlds because it obtains in all possible worlds, which is a tautology and thus not an explanation. Eh?

'Construed as' amounts to 'defined as'. Of course that turns out to be tautological. It's a definition, not an explanation.

An explanation would be something one would offer in defense of its being a good definition.

[Dominus Paradoxum]

But what I was trying to show was that the possible worlds construal doesn't capture the ordinary notion of necessity. With the ordinary notion, it makes perfectly good sense to ask why something obtains in all possible worlds and the common sense answer is, because it's necessary. According to common sense it would be an explanation to say that it's true in all possible worlds because it's necessary and, and if possible worlds modalism doesn't allow that answer that's a defect in possible worlds modalism. You have to understand that, according to possible worlds modalism, they're literally can't be any reason why something is true in all possible worlds.

[The Helmetmaker]

Originally posted by Dominus Paradoxum
But what I was trying to show was that the possible worlds construal doesn't capture the ordinary notion of necessity. With the ordinary notion, it makes perfectly good sense to ask why something obtains in all possible worlds and the common sense answer is, because it's necessary. According to common sense it would be an explanation to say that it's true in all possible worlds because it's necessary and, and if possible worlds modalism doesn't allow that answer that's a defect in possible worlds modalism. You have to understand that, according to possible worlds modalism, they're literally can't be any reason why something is true in all possible worlds.


Which makes the possible worlds modality the uptown cousin of arguments from incredulity: "I can't imagine any scenario in which X is true (or false), and so X must be true (or false)."

I don't think it's clear that the set of possible worlds which can be constructed in a given possible world must be identical to the sets of possible worlds which can be constructed in all possible worlds. Perhaps the reason something is true in all possible worlds isn't a reason, but artificial a prioris.


The Helmetmaker

[Phanes]

Originally posted by Dominus Paradoxum
Also, according to modal realism all possible worlds necessarily exist. But, according to modal realism, this can only mean that all possible worlds exist in all possible worlds, which is nonsense.

I don't understand this part. Possible worlds do not "exist" in the same way the word is ordinary used. To say that a possible world exists is just to say that it is possible, which is obviously tautological. Likewise, "all possible worlds necessarily exist" would mean "all possible worlds are necessarily possible," which looks fine (if awkwardly put) to me.

Also, though I haven't critically thought about it just now, I suspect your "tautological problem" exists for any conception of necessity, modal or otherwise, because it's just a reflection about definitions (e.g. "exists in all possible worlds" really is the definition of necessity in modal logic, not some kind of consequence).

[Dominus Paradoxum]

Possible worlds do not "exist" in the same way the word is ordinary used.

According to David Lewis, they do. In modal realism other possible worlds are just as concrete as the actual world, they just happen to be disconnected to it in spacetime. 'Actual' is thus an indexical term which means "related to the speaker in spacetime"

Also, though I haven't critically thought about it just now, I suspect your "tautological problem" exists for any conception of necessity, modal or otherwise, because it's just a reflection about definitions (e.g. "exists in all possible worlds" really is the definition of necessity in modal logic, not some kind of consequence).

Right. Which is why I'm beginning to suspect that the concept of necessity is fictive.

[Phanes]

Originally posted by Dominus Paradoxum
According to David Lewis, they do. In modal realism other possible worlds are just as concrete as the actual world, they just happen to be disconnected to it in spacetime.

According to A. Prior they don't. :p

And I'm inclined to agree. What's so special about the "actual" world if it's just a relative conception? Any world with a perceiver in it would be "actual" (at least for those perceivers).

Maybe it's an interesting idea, but it still sounds like abuse of language to me.

[Witt]

Possible worlds is not to be take literally. Mars or Vulcan are possibilities only if they contain the same entities of our actual word but in different arrangements. Possible universes of discourse is a better expression.

Necessary propositions are those which are true in all possible universes of discourse.

We do not admit impossible objects in any admissable (world)
or universe of discourse.

The present king of France does not exist in our world, but, it clearly does exist in the world of a different time.

That which is and is not, does not exist in any possible world, that is, it does not exist in any universe of discourse.

Witt

[davidm]

Originally posted by Dominus Paradoxum
According to David Lewis, they do. In modal realism other possible worlds are just as concrete as the actual world, they just happen to be disconnected to it in spacetime. 'Actual' is thus an indexical term which means "related to the speaker in spacetime"





Why does he think other possible worlds are concrete? Several years ago I bought his book, "On the Plurality of Worlds," which made this argument, but being a philosophy dunce, I couldn't follow it. It was the first time I ran across the word iff and I immediately assumed poor proofreading on the part of the publishers. :)

But really, why should anyone take this argument seriously? As I recall from the book he even maintained that there must be other concrete worlds with supernatural elements in them.

[Bilbo]

quote:
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Originally posted by Dominus Paradoxum
According to David Lewis, they do. In modal realism other possible worlds are just as concrete as the actual world, they just happen to be disconnected to it in spacetime. 'Actual' is thus an indexical term which means "related to the speaker in spacetime"
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Why does he think other possible worlds are concrete? Several years ago I bought his book, "On the Plurality of Worlds," which made this argument, but being a philosophy dunce, I couldn't follow it.
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Lewis has attempted to develop a theory of modality within a generally physicalist framework. He's not primarily "arguing" for the idea that his worlds must be concrete (though of course he does pick at some percieved difficulties with ersatz or "abstractionist" theories of worlds), rather, he's stipulating that this is how he intends to use the terminology.

On a corrective note, it should be pointed out that *modal realism* does not require (or even suggest) Lewis' concretist account of worlds. This should dispel some of the familiar suspicions that the former is somehow tied up in the latter. In fact, contrary to Stalnaker's dubbing of Lewis as an "extreme modal realist", some fairly sensible and straightforward arguments have been made by others that Lewis isn't a realist about worlds at all. If modal realism is a claim about anything interesting, it should involve a robust claim about the the *kinds* of things there are.

So given a traditional use of terms and understanding of concepts, modal realism and Lewis's concretism are independant theses, and the problems associated with one don't usually carry over to the other.

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But really, why should anyone take this argument seriously?
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Perhaps you can clarify what you have difficulty taking seriously; the claim that there are worlds, or the claim that worlds are concrete.

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As I recall from the book he even maintained that there must be other concrete worlds with supernatural elements in them.
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The idea that Lewis endorses any sort of supernaturalism with regards to his theory of worlds seems quite mistaken. Lewis doesn't believe in any more metaphysical entities than most other physicalists (where "more" is construed in a qualitative, rather than quantitative sense). See chapter four of his book Counterfactuals (pg 87) for elaboration of this point.


Regards,

Bilbo.

[davidm]

Originally posted by Bilbo
quote:
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Originally posted by Dominus Paradoxum
According to David Lewis, they do. In modal realism other possible worlds are just as concrete as the actual world, they just happen to be disconnected to it in spacetime. 'Actual' is thus an indexical term which means "related to the speaker in spacetime"
--------------------------------------------------------------------------------
Why does he think other possible worlds are concrete? Several years ago I bought his book, "On the Plurality of Worlds," which made this argument, but being a philosophy dunce, I couldn't follow it.
--------------------------------------------------------------------------------

Lewis has attempted to develop a theory of modality within a generally physicalist framework. He's not primarily "arguing" for the idea that his worlds must be concrete (though of course he does pick at some percieved difficulties with ersatz or "abstractionist" theories of worlds), rather, he's stipulating that this is how he intends to use the terminology.

On a corrective note, it should be pointed out that *modal realism* does not require (or even suggest) Lewis' concretist account of worlds. This should dispel some of the familiar suspicions that the former is somehow tied up in the latter. In fact, contrary to Stalnaker's dubbing of Lewis as an "extreme modal realist", some fairly sensible and straightforward arguments have been made by others that Lewis isn't a realist about worlds at all. If modal realism is a claim about anything interesting, it should involve a robust claim about the the *kinds* of things there are.

So given a traditional use of terms and understanding of concepts, modal realism and Lewis's concretism are independant theses, and the problems associated with one don't usually carry over to the other.

--------------------------------------------------------------------------------
But really, why should anyone take this argument seriously?
--------------------------------------------------------------------------------

Perhaps you can clarify what you have difficulty taking seriously; the claim that there are worlds, or the claim that worlds are concrete.

--------------------------------------------------------------------------------
As I recall from the book he even maintained that there must be other concrete worlds with supernatural elements in them.
--------------------------------------------------------------------------------

The idea that Lewis endorses any sort of supernaturalism with regards to his theory of worlds seems quite mistaken. Lewis doesn't believe in any more metaphysical entities than most other physicalists (where "more" is construed in a qualitative, rather than quantitative sense). See chapter four of his book Counterfactuals (pg 87) for elaboration of this point.


Regards,

Bilbo.

Thanks for your reply. I have difficulty taking seriously the claim that the worlds are concrete.

Your description of what Lewis said surprises me somewhat. I always thought that he was an extreme modal realist, and for him this meant that concrete worlds existed. They just wouldn't be actual "for us." But they would be actual to their own inhabitants, if any. Possibly I've misconstrued his argument, but then I think others have as well.

I do recall from his plurality of worlds book a statement about worlds with "spirits and entelechies." If he is in fact insisting that worlds different from our own are concrete, I don't know how else you can interpret this statement, but that there are concrete worlds with supernatural elements.

[Bilbo]

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Thanks for your reply. I have difficulty taking seriously the claim that the worlds are concrete.
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Many philosophers will join you. In fact, the coherance of Lewis'
theory has frequently been questioned on this point.

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Your description of what Lewis said surprises me somewhat. I always thought that he was an extreme modal realist, and for him this meant that concrete worlds existed.
-----------------------------

I'm not sure what you're refering to in the first sentence, but you're not alone in thinking that Lewis is an extreme modal realist. You are correct when you suggest that, for him, this means that the concrete objects he sometimes calls "worlds" do in fact exist. In other words, when he says: "there are possible worlds", he expects us to take the "there are" literally; as a straightforward objectual quantification over the things he's discussing.

I alluded to those who have called into question the *realism* in Lewis' "modal realism" merely to correct the persistent misconception that Lewis is the exemplar of this view; that he is its outstanding spokesman. The reality of the matter is that he is regarded by his peers as a voice in the wilderness. Few modal realists embrace the more significant elements of his theory as their own.

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They just wouldn't be actual "for us." But they would be actual to their own inhabitants, if any. Possibly I've misconstrued his argument, but then I think others have as well.
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I don't think you've misconstrued his claims. He certainly views himself as a modal realist (ie - he believes that objects of a certain sort really do exist). Your account of his indexical analysis of 'actuality' looks spot on as well.

----------------------------------------------------
I do recall from his plurality of worlds book a statement about worlds with "spirits and entelechies." If he is in fact insisting that worlds different from our own are concrete, I don't know how else you can interpret this statement, but that there are concrete worlds with supernatural elements.
----------------------------------------------------

Lewis anticipates some objections to his theory. He writes:

"A second objection concerns spirits, and episodes in the mental lives of spirits, which are traditionally supposed to be outside of space. However sure we are that no such deficient things are worldmates of ours, is it not at least possible that the traditional story might be true? If so, then some world is populated by such spirits. But that is no objection. I do not say that all worlds are unified by spatiotemporal interrelatedness in just the same way. So the interaction of a world of spirits might be looser than that of a decent world like ours. If the spirits and their doings are located in time alone, that is good enough. (To make sense of that, maybe time and space would have to be more seperable at the world of spirits than they are at our world; but that is surely possible.) I can even allow marvellous Spirits who are spatiotemporally related to other things by being omnipresent - for that is one way among others to stand in spatiotemporal relations. I am not sure why I need to defend the possibility of spirit tales - after all, people have been kown to accept impossible theories, as witness naive set theory - but in fact I think I give them at least as much room in logical space as they deserve." - On the Plurality of Worlds. (Oxford, UK: Basil Blackwell, Ltd., 1986). p.73

While this passage admittedly looks a little suspicious, I don't think there's much here that a physicalist needs to fuss over. Lewis' views concerning space-time and object mereology are both highly nuanced and eclectic. Since most of his non-modal ontology regarding properties, numbers, sets, the part-whole relation, tropes, and laws, comport with views espoused by other well known physicalists like D.M. Armstrong and W.V Quine (his mentor), it doesn't seem sensible to me to interpret him as suddenly changing his tune to "supernaturalism" in mid-modal stride.

Perhaps light can be shed on this passage by recalling that according to Lewis, the traditional abstract/concrete distinction is rather dubious. For him, the distinction between material objects, and non-spatio-temporal objects or parts (in this case - "spirits") is not as clear cut as we usually suppose. So while Lewis is tentatively agreeable to calling his worlds "concrete", he is quite flexible about whether his worlds must all be concrete *in the same way*. What does seem fairly clear to me is that his use of "spirits" here doesn't coincide in any substantial way with what theists or "supernaturalists" typically intend when using that term.

I think these considerations (to say nothing of his explicit testimony throughout his published work) are sufficient to quell suspicions that supernaturalism is entailed by his views on modality.

Regards,

Bilbo

[davidm]

Originally posted by Bilbo

I don't think you've misconstrued his claims. He certainly views himself as a modal realist (ie - he believes that objects of a certain sort really do exist). Your account of his indexical analysis of 'actuality' looks spot on as well.

Ah, thanks again for the reply, Bilbo. I missed it earlier.

I'm still puzzled as to why he believes this. This is where I'm sure I'm missing something due to a misunderstanding of the philosophy behind it. (Recall I'm a philosophy dunce.) I'm asking, why does he believe in these concrete worlds that really exist, real in the sense that they are real to their inhabitants? I take at face value this description of the philosophy by Peter J. King, a philosophy instructor at Oxford:

1. Possible worlds exist -- they are just as real as our world;

2. Possible worlds are the same sort of things as our world -- they differ in content, not in kind;

3. Possible worlds cannot be reduced to something more basic -- they are irreducible entities in their own right.

From these three claims (and from the second in particular) we can see that, when we talk of our own world as being the only actual world, we cannot be asserting that our world has a special property not found in (or instantiated by) any other world - the property of actuality - but that we must be using the term `actual' much as we use the term `here' or `now' -- to indicate our position. This gives us Lewis's fourth doctrine:

4. `Actual' is indexical. When we distinguish our world from others by claiming that it alone is actual, we mean only that it is ours -- we live here.

These four claims are not only central to Lewis's approach, they are essential to it

So to say that these other worlds are not concrete, would be like saying that Boston is not concrete because I live in New York.

It is such an audacious claim that it has always intrigued me, and my interest was rekindled by the fact that Max Tegmark, a physicist, now believes that such worlds do in fact exist, that there is evidence for them and a proper theory can be made to test for them. In writing about this idea, he mentioned Lewis. But that is science and not philosopy. I'm interested in the philosophical underpinning that made this idea compelling to Lewis.

Lewis anticipates some objections to his theory. He writes:

"A second objection concerns spirits, and episodes in the mental lives of spirits, which are traditionally supposed to be outside of space. However sure we are that no such deficient things are worldmates of ours, is it not at least possible that the traditional story might be true? If so, then some world is populated by such spirits. But that is no objection. I do not say that all worlds are unified by spatiotemporal interrelatedness in just the same way. So the interaction of a world of spirits might be looser than that of a decent world like ours. If the spirits and their doings are located in time alone, that is good enough. (To make sense of that, maybe time and space would have to be more seperable at the world of spirits than they are at our world; but that is surely possible.) I can even allow marvellous Spirits who are spatiotemporally related to other things by being omnipresent - for that is one way among others to stand in spatiotemporal relations. I am not sure why I need to defend the possibility of spirit tales - after all, people have been kown to accept impossible theories, as witness naive set theory - but in fact I think I give them at least as much room in logical space as they deserve." - On the Plurality of Worlds. (Oxford, UK: Basil Blackwell, Ltd., 1986). p.73

While this passage admittedly looks a little suspicious, I don't think there's much here that a physicalist needs to fuss over. Lewis' views concerning space-time and object mereology are both highly nuanced and eclectic. Since most of his non-modal ontology regarding properties, numbers, sets, the part-whole relation, tropes, and laws, comport with views espoused by other well known physicalists like D.M. Armstrong and W.V Quine (his mentor), it doesn't seem sensible to me to interpret him as suddenly changing his tune to "supernaturalism" in mid-modal stride.

Perhaps light can be shed on this passage by recalling that according to Lewis, the traditional abstract/concrete distinction is rather dubious. For him, the distinction between material objects, and non-spatio-temporal objects or parts (in this case - "spirits") is not as clear cut as we usually suppose. So while Lewis is tentatively agreeable to calling his worlds "concrete", he is quite flexible about whether his worlds must all be concrete *in the same way*. What does seem fairly clear to me is that his use of "spirits" here doesn't coincide in any substantial way with what theists or "supernaturalists" typically intend when using that term.

My interpretation of his stand, and I think this is what you are saying too, is that other worlds could be radically different in their properties, and in their relations between the whole and the parts, from our own. This could allow for something very like what we, in our own world, would call "spirits," entities not possible in our world but possible in worlds with different basic laws and properties.