Oh, very good. — Ludwig V

Pleased someone notes the drollery! :grin:

a) that the actual world is the one in which we are constructing the possible worlds and the point of view from which we are surveying them and identifying which world we wish to treat as actual — Ludwig V

Yep. Hence the sometime definition of truth simpliciter as "true in w₀"... All of our modal logic is "true in w₀"!

b) that we do not choose that world - we are lumbered with it - even thrown into it. — Ludwig V

Pretty much.

What we don't have here is any inconsistency...

Leastwise, none I can see.


I was thinking about the "books" analog the other day, but can't now recall what it was I thunked. I think something like that is going on in the article, with the tree differing accounts of what possible worlds are; and I think it is somehow off-centre. But I haven't yet worked out quite how.

Part of the problem is that the books analogy and the three accounts picture the world as complete.

What does “water” mean? "Water" means different things to different people. To a scientist, "water" is necessarily H2O. To me, "water" is necessarily wet, in that if not wet it cannot be water. To a linguist, “water” is necessarily a noun. There is no one meaning of “water”, though each meaning is necessary within its own context.
— RussellA
And yet all these people can communicate. How is that possible? There must be common elements to all these different meanings that enable communication across contexts. Those common elements are what we might call ordinary life, which is the common context that links all three people. — Ludwig V

I would disagree with “to the scientist “water” is necessarily H2O” but I am not going to rehash everything I have said up to this point.

But I would like to add further criticism to this idea that water is essentially H2O. Take the following three types of water (and I could name many more)

1. “Sea water”
2. “Purified water”
3. “Purified heavy water”

Sea water >96% H2O unsafe to drink

Purified water >99% H2O safe to drink but long term use may deplete essential minerals

Purified heavy water >99% D2O ok to drink in very small quantities but very hazardous in larger amounts

All use the term “water” but there is no common essence between them.

See my post

This does not show any inconsistency with the article, nor any inconsistency in treating actual as an indexical.

Can you complete your argument? — Banno

I already did, by pointing to, and discussing, the supplementary article Classical Possibilism and Lewisian Possibilism. It's pretty explicit when it says: :"Unfortunately, things often get a bit murky in discussions of Lewis because, as noted in thesis 5, he does not use the word “actual” to indicate the mode of being that we enjoy (and that, according to the classical possibilist, some things do not) but, rather, to indicate this world and its inhabitants. "

Read the whole of my post, I see no reason to repeat it.

, that quote doesn't seem to do what you think it does.

But, fine, carry on.

Please explain what you think I got wrong.

Well, I do't see an argument that has as it's comnclusion:

The notion that "actual" is indexical is not consistent with the terminology in the SEP article, The Possibilism-Actualism Debate: — Relativist

So we agree that for Possibilists reality includes possibilia, things that could exist but do not actually exist, that there’s a broader realm beyond the concrete world. And that Actualists suppose only what actually exists counts as real. There’s no domain of merely possible entities. And that Lewis treates "actual" as indexical. To show inconsistency, one would have to demonstrate that the SEP article’s definitions cannot accommodate an indexical sense of “actual”, or that indexical “actual” violates SEP’s logic. I don't see that here.

But as noted, I'm more interested in the main article here than in this side issue. Once we have an agreed view on what the possibilities are for possible worlds, then we might better treat the possible and the actual.

Small steps.

Lewis does believe that all possible worlds are actual worlds, but that's not a common view. Lots of philosophers disagree about that, but still use possible world semantics to discuss counterfactuals. Whether or not those counterfactual worlds are possible is debatable - but "possible" can apply to past, present, and future. — Relativist

Yes, I thought that's what we were talking about, Lewis' interpretation where all possible worlds are actual.

In everyday discourse it's ambiguous, but it appears to me that among philosophers, there's no ambiguity about what it means. There are controversies, but not about the basic definition. — Relativist

Not at all, like all the terms of modal logic, there is a big difference between ontological meaning and modal logic meaning. That is the ongoing discussion I've had with Banno over the meaniong of "the actual world".

What this shows is that Meta's way of talking is incompatible with the formal account. — Banno

Obviously.

He's not offering an alternative theory. — Banno

I offered an alternative theory. It involves a real ontology of time, and a separation between ontological possibility, statements of epistemological possibility, and counterfactual statements which are not possibilities at all, being statement so things which are actually impossible. That's three distinct categories.

For the rest of us, some proposal is contingent if and only if it is true in some, but not all, possible worlds. — Banno

Relaitivist and I were talking about "contingent things", not "contingent proposals". @Relativist, see what I mean about the ambiguity?

It is as if you were arguing that "over there" is meaningless, because it can be made to refer to any place at all. — Banno

You're ignoring the other half of the conditions. The meaninglessness was dependent on referring to everything as actual, and also without a definition for "actual". That's the situation Relativist and I were discussing concerning Lewis' interpretation of possible worlds. Every possible world is an actual world, and Relativist added that the world we perceive is an actual world, therefore everything is "actual", and I said that if everything is actual, then without a definition, "actual" is meaningless.

This shows very clearly and precisely, in a nutshell, the significant and substantial problem with your understanding of possible world semantics. In standard modal logic, the term “actual world” is an indexical label applied to one world in the model—it does not make any ontological claim about that world being the only real or “ontologically actual” world. It is a convenient reference point for evaluating modal statements, just as “here” or “now” is in ordinary language. — Banno

Banno, did you not read the SEP on truth conditions? The actual world of the modal model must "in fact" be the actual world. This means it must be the ontological actual world. This will be the third or fourth time I've produced this quote. Are you blind, or just unable to understand English?

(ii) its designated “actual world” is in fact the actual world, — SEP

How do you interpret "is in fact the actual world", in any way other than 'is the ontologically actual world'? That is an ontological statement. It does not state as the truth condition that the designated actual world must be the designated actual world, it states that the designated actual world "is in fact the actual world". Do you see that, and understand what it means? That is why Lewis proceeds to propose that each possible world is a concrete world, just like the one we designate as "the actual world", because we know "the actual world" ontologically as a concrete world, and the truth condition requires that the actual world in the modal model must "in fact", be the actual world. Therefore he concludes that all the possible worlds must be concrete worlds, just like the one we know.

You confusion comes from thinking that the world given the title w₀ in a modal interpretation must be our world - the confusion of the modal and the metaphysical. Think I've mentioned that before. — Banno

According to the SEP, the modal "actual world", must in fact, be the actual world. If you maintain that there is another "actual world", what you call the "metaphysically actual world", then to accept the modalism, you must reject the truth of the metaphysically actual world. It must be an illusion, because the modal actual world is "in fact", the actual world, and the metaphysical world is different, as you assert, so the metaphysical "actual world" must be fictional.

Yes, cheers - understood. I find it easier to answer these odd little objections than to move on with the harder stuff of the article, so I find myself somewhat distracted. There's a chance that the explanations I'm giving will help folk see the direction the article is taking. It's already very clear that Meta - for whom you started this thread - is for whatever reason incapable of following the discussion. But others may be coming along. — Banno

You think that this is the easier stuff, but you seem completely incapable of understanding it. Look at the meaning of "is in fact the actual world", for example. Why ignore the "is in fact" part, as it is a critical truth condition? Accept what the article says, and get on with the Idealism of modal logic. Instead, you keep insisting that there is another "actual world", the metaphysically actual world. But the "metaphysically actual world" is ruled out, as a fiction, when it is stipulated that the modal actual world is "in fact" the actual world. So, the easy part puts us into the idealist framework. Now, having gotten beyond the easy part, we must now proceed within that idealist framework, otherwise our interpretations are bound to be badly mistaken.

To show inconsistency, one would have to demonstrate that the SEP article’s definitions cannot accommodate an indexical sense of “actual”, or that indexical “actual” violates SEP’s logic. I don't see that here. — Banno

I agree it doesn't violate the logic.

ok.

I see what you mean. Thanks for explaining.

I offered an alternative theory. — Metaphysician Undercover

Well, no. What you have offered, a set of assertions, isn’t a theory on a par with possible-worlds semantics. It doesn't provide a formal semantics. Possible-worlds semantics gives precise truth-conditions for modal claims, compositional rules for complex sentences, and a mathematically explicit structure (models, accessibility relations, evaluation clauses). Your proposal is a taxonomic distinction, a mere set of metaphysical labels separating ontology, epistemology, and counterfactual talk, without rules that determine when modal statements are true or false, or how they interact logically. It replaces a working semantic framework with intuitive metaphysical assertions, so it cannot do the same explanatory or inferential work.

The rest is layered confusion on your part.

Might not be a bad idea to go over the terms being used, since it seems there is some confusion.

Exists
A thing exists if it is in the domain of a world. That is, if it can be used in an existential quantification. Existence is what the existential quantifier expresses. Things can exist in one world and not in another. One point of difference between Lewis and Kripke is that for Lewis things exist only within a world, while for Kripke the very same thing can exist in multiple worlds.

A thing that exists is also possible.

In Kripke a thing can exist and not be actual or concrete.
In Lewis if a thing exists then it is concrete, and actual in some world.

Possible
It's possible if it's “true in at least one accessible world”.

Something might be possible and yet not exist - by not existing in w₀ but in some other possible world

Simialrly, a sentence is possible if it is true in some accessible world.

Actual
Actual is indexical. It works like here, or like now. We designate a world as the actual world, w₀, and then the things that exist in that world are actual.

In modal logic being actual is a label. In metaphysics being actual is usually a special ontological state. Lewis rejects this, since everything is actual in some world.

Contingent
A modal variability across worlds, something is contingent if it exists in some, but not all, possible worlds. And similarly, sentences are contingent if ◇P ^ ◇~P. If it exists in all possible worlds it is necessary. If it doesn't exist in any world, it is impossible.

Contingency is assessed modally, not temporally. So an event can occur and still modally contingent.
The fact that it happened does not make it necessary.

Concrete
This one is less clear. If something is physical, spatiotemporal, or causal it might be considered concrete.

In Lewis' system everything is concrete, in a world that is spatiotemporally separate and distinct from every other possible world.

In actualist accounts, only the things in the actual world are concrete. The other stuff is abstract.


Real
A claim of Metaphysical status. In Lewis something is real if it exists. In actualist accounts it is real if it both exists and is actual.


What fun.

Nice, I arrived just as someone was defining terms.

Just today, I've been in conversation about things like existence, necessary/contingent things, and possible worlds. By your definition of existence, it seems that things exist relatively, particularly in relation to some possible world. This is something I resonate with, but I figure there's a difference in how I'm thinking about it.

One thing that I'm not sure is addressed in possible world semantics, is this concept of a "meta-world". So, if there exists possible worlds, are they all existing together as a collection in some world that contains them all? Is that the wrong way to think about it, and how so? Does it even make sense to say worlds exist or don't exist, as it seems you're defining existence to entities within worlds rather than the worlds themselves?

For my own part, the possiblism/actualism debate is much ado about very little. — Banno

I find it keeps slipping from my grasp.

What we don't have here is any inconsistency... — Banno

It wasn't that I saw an inconsistency, it was just that I didn't see how it fitted together. However, doesn't the idea that we can choose which world is actual conflict with the definition of "truth simipliter" as "true in w₀"? Or, better, if we choose to locate the world in which we construct the possible worlds in w₀, (which isn't a problem in itself) doesn't that conflict with the idea that we find ourselves in that world, and do not choose it. That's why I've been trying to locate that move in a different context from the choices we can make about other possible worlds. Don't we need to mark a distinction between that world and any world we choose to treat as actual for purposes of logical analysis? just labelling it metaphysical doesn't explain anything unless we have a good definition of "metaphysical".

Sea water >96% H2O unsafe to drink
Purified water >99% H2O safe to drink but long term use may deplete essential minerals
Purified heavy water >99% D2O ok to drink in very small quantities but very hazardous in larger amounts
All use the term “water” but there is no common essence between them. — Richard B

I don't have a problem with this. It all goes back to the concept of a game as a network of common elements - more like a rope (which has no thread running through its entire length, but is composed of shorter threads that overlap and interlock) than a filament (like a fishing line) which isn't made up of strands. But it's not an actual argument, more of a challenge. On the other hand, so far as I know, no-one has yet risen to it, so it is very persuasive. Kripke is the exception here. No doubt he would sweep it under some carpet. But that doesn't mean it is not true.

Contingent
A modal variability across worlds, something is contingent if it exists in some, but not all, possible worlds. And similarly, sentences are contingent if ◇P ^ ◇~P. If it exists in all possible worlds it is necessary. If it doesn't exist in any world, it is impossible. — Banno

So what do you do with Kripke's Aristotle that necessarily names Aristotle in all worlds in which Aristotle exists? (Is it really impossible that Aristotle could not have had some other name, if he was born at the right time of the right parents and did all the right things?)

So, if there exists possible worlds, are they all existing together as a collection in some world that contains them all? — QuixoticAgnostic

And yet all these people can communicate. How is that possible? There must be common elements to all these different meanings that enable communication across contexts. Those common elements are what we might call ordinary life, which is the common context that links all three people. — Ludwig V

Kripke’s solution in his Theory of Naming is that there is an historic causal chain from a something that has a name, such as Aristotle, to the initial baptism of a something given that name, such as Aristotle’s parents naming their baby Aristotle. In a sense, this baptism is the same as JL Austin’s performative utterance. Kripke’s solution bypasses any metaphysical problems as to the essence of Aristotle. The name Aristotle is just a tag to something else, and in this case that something baptised Aristotle.

Wittgenstein’s approach in Philosophical Investigations is similar. Names exist within the context of a Form of Life, “the shared background of human cultural practices, activities, and ways of living that provide the context within which language and meaning operate” (Wikipedia). When the assistant walks onto a building site for the first time, the assistant may see the builder pick something up and say “slab”. For the assistant, this is the initial baptism of something given the name “slab”. Subsequently, when the builder says to the assistant “slab”, the assistant knows what the builder is referring to. As before, the assistant does not need to know about the essences of slabs. “Slab” just means a tag in an historic causal chain going back to an initial baptism.

Similarly with “water”, as you say, me, the scientist and the linguist share a common Form of Life, where the meaning of words is understood through historical causal chains back to a common source. These common sources may be, for example, dictionaries, school, television, newspapers, etc.

But Lewis' interpretation appears to be that each possible world "is" an actual world. — Metaphysician Undercover

Your statement is incomplete as it needs to add “for whom”.

For Lewis, it seems that between our world and possible worlds no world is especially favoured. Therefore, for anyone living in a world, their world is the actual world.

For us, we live in the actual world. For us, other worlds are possible worlds, but for anyone living in such a possible world, they would also consider their world to be the actual world.

A possible rewording would be “But Lewis' interpretation appears to be that each possible world "is" an actual world for the inhabitants of that world”

But if the sun is actually shining, then although you don't know this fact, it is physically, metaphysically, and logically impossible for the sun to not be shining at that point of time. (Law of noncontradiction). — Relativist

There are two aspects, language and facts in the world.

“The sun is shining” is true IFF the sun is shining.

By the Law of Non-Contradiction, it is logically impossible for the fact in the world i) the sun is shining and the fact in the world ii) the sun is not shining.

However, in language, the Law of Non-Contradiction does not apply to the propositions “the sun is shining” and “the sun is not shining”.

===========================================================================

Yet another issue: is the sun shining at that point of time a contingent fact, or a necessary fact? — Relativist

It depends whether you have a belief in Determinism, where it would be a necessary fact, or had a belief in Indeterminism, where it would be a contingent fact.

Wikipedia
Determinism is the metaphysical view that all events within the universe can occur only in one possible way.
Indeterminism is the idea that events are not caused, or are not caused deterministically. It is the opposite of determinism and related to chance.

do what to get my head around the section Irreducible Modality and Intensional Entities, and I don't think the material there especially deep. But finding the right words will take time. — Banno

Looks daunting. I'll see if I can get through it.

Possible-worlds semantics gives precise truth-conditions for modal claims, compositional rules for complex sentences, and a mathematically explicit structure (models, accessibility relations, evaluation clauses). — Banno

You demonstrate the problem with possible world semantics very well, right there. The nature of possibility is such that it is impossible to give "precise truth-conditions for modal claims". That's the fundamental reality of what is referred to by "possibility", it violates the basic truth conditions of the law of non-contradiction, or the law of excluded middle. This was demonstrated by Aristotle with examples like the possible sea battle.

So possible world semantics attempts to do the impossible, give "precise truth-conditions for modal claims". It's far better that we respect reality, and deal with possibility with strategies like "probability", than to proceed under the sophistic illusion of "precise truth conditions" which is created by possible world semantics.

For us, we live in the actual world. For us, other worlds are possible worlds, but for anyone living in such a possible world, they would also consider their world to be the actual world.

A possible rewording would be “But Lewis' interpretation appears to be that each possible world "is" an actual world for the inhabitants of that world” — RussellA

I don't know Lewis; principles too well. Do you think that it's possible for the different individuals referred to by "us", live in different possible worlds? How would we be able to communicate, and make sense of the things around us, when contradictory things would be true for each of us? Without the unity produced by agreement, could there be an "us"?