speaking of worlds as simply "possible" allows one to confuse logical, physical and ontological possibility. — Dfpolis

...distinctions whose advocates can't specify what they mean by them.

You believe in an un-acknowledged and unsupported assumption that the physical world that we live in is the "actual", "existent", "physical" and "real" one, in some (unspecified) sense in which the infinitely-many other possibility-worlds aren't.

David Lewis, more realistically, defined "the actual world" as the world in which the speaker resides.

And then, while advocating the unique existence, actuality and reality of our own physical world, people then wonder why there is that thing that they assert their belief in. :D

What we can all agree on is that there are abstract implications, in the sense that we can refer to them and mention them.

There's no reason to ask why there are such things, and there's no reasons to claim that they're "real" or "existent", whatever that would mean.

There are infinitely-many complex systems of inter-referring abstract implications about hypothetical propositions about hypothetical things, with the many consistent configurations of mutually-consistent hypothetical truth-values for those hypothetical propositions.

...with no particular reason to believe that any of the antecedents of any of those implications are true.

Some of those abstract logical systems fit the same description as your experience. There's no reason to believe that your experience is other than such an abstract logical system. I call such systems "hypothetical life experience stories".

If you claim that this physical world is more than the setting for the hypothetical logical system that is your experience-story, then in what respect to you think that this physical world is more than that.

More "actual", "existent" or "real"? Then what do you mean by those words.

In what context do you want or believe this physical universe to be "existent", other than its own?

I don't claim that this physical universe and its things don't have some other (unspecified) kind of "existence" (whatever that would mean), as a superfluous, unverifiable, unfalsifiable brute-fact, alongside of, and duplicating the events and relations of, one of the infinitely-many abstract logical-systems that I referred to above.

Do you believe in unparsimonious brute-facts and unverfiable, unfalsifiable propositions?

Michael Ossipoff

What makes it the case that one thing in one possible world and one thing in another possible world are the same thing?

Let’s say that I’m the eldest of two brothers in the actual world and that there’s a possible world where my parents have two daughters and a possible world where my parents have two sons. Which child, if either, am I in each world? Is it simply a matter of stipulation? Do we just say that I’m one or the other (or neither)?

Perhaps in the first possible world it’s me and my brother if we were female? Perhaps in the fourth possible world it’s two different children who happen to look and behave like my brother and I do in the actual world?

Edit: And, of course, what makes it the cases that these people are my parents in each world?

What makes it the case that one thing in one possible world and one thing in another possible world are the same thing? — Michael

It's the exact same sort of thing that makes it the case that "A" and "B" are numerically the same in the actual world: criteria of identity and individuation. Those criteria vary as a function of the sorts of things that are at issue. Planets, persons, sports teams, cell lineages, ocean waves, etc., have different principles of individuation. Sometimes those principles mainly are matters of social convention but they can also be, in part, objects of scientific inquiry.

So, what makes it the case that, in the possible world where you catch the flu tomorrow, say, you are the very same individual human being than you are in the actual world (in which you don't catch the flu), is the very same principle of individuation in accordance with which we judge that, in the actual world, people don't cease to exist and their persisting bodies come to materially constitute numerically distinct human being at a later time just because they catch a bug. (Maybe there is some alien race, somewhere in the universe, where personhood conventions are different and individual organisms who catch a bug are deemed to be turned into a numerically different person or animal).

Let’s say that I’m the eldest of two brothers in the actual world and that there’s a possible world where my parents have two daughters and a possible world where my parents have two sons. Which child, if either, am I in each world? Is it simply a matter of stipulation?

There are possible worlds where your parents have two sons neither of which is you. This is equivalent to saying that it is possible that you would not have been born but that your parents would nevertheless have had two sons.

Do we simply say that I’m one or the other (or neither)?

Perhaps in the first possible world it’s me and my brother if we were female? Perhaps in the fourth possible world it’s two different children who happen to look and behave like my brother and I do in the actual world?

Your puzzle stems from the question: what it is that distinguish a possible world where a son is born to your parents that looks and behaves just like you, but isn't you, from a world in which this son is you? Those two scenarios are indeed metaphysically distinct and, what distinguished them precisely, are our ordinary criteria of identity of persons as they are meant to apply in the actual world. It's possible, though, that our criteria of identity of persons aren't fine grained enough to determine whether or not your would have been the same person if the sperm and ovum that your are issued from had combined at a different time, or if the sperm itself, say, has been a different one that accidentally shared the very same sequence of nucleotides with the actual one, etc. That just means that our ordinary concept of a person, and its associated criteria of identity and individuation, isn't meant to deal with such unlikely possibilities since there is little pragmatic point in dealing with them.

Your puzzle stems from the question: what it is that distinguish a possible world where a son is born to your parents that looks and behaves just like you, but isn't you, from a world in which this son is you? Those two scenarios are indeed metaphysically distinct and, what distinguished them precisely, are our ordinary criteria of identity of persons as they are meant to apply in the actual world. It's possible, though, that our criteria of identity of persons aren't fine grained enough to determine whether or not your would have been the same person if the sperm and ovum that your are issued from had combined at a different time, or if the sperm has been a different different one that accidentally shared the very same sequence of nucleotides, etc. That just means that our ordinary concept of a person, and its associated criteria of identity, isn't meant to deal with such unlikely possibilities since there is little pragmatic point in dealing with them. — Pierre-Normand

Then perhaps if we use a simpler example of an inanimate object. In another possible world the Taj Mahal was built using different materials, or at a different location, or with a different architecture. Does that make sense? Is it just a matter of stipulation that we consider them the same thing (or different things) in each possible world?

What makes it the case that one thing in one possible world and one thing in another possible world are the same thing? — Michael

As David Lewis pointed out, there's no need to say that those identical things (or persons) in other possibility-worlds are the same person. Instead, call them "counterparts" of that thing or person.

It depends on how you define "same". Lewis's suggestion was that "same" doesn't meaningfully and usefully apply to someone or something in a different possibility world, It's a different world, necessarily with different (even if identical) things.

After all, usefulness is a consideration when defining a word.

Michael Ossipoff

It's the exact same sort of thing that makes it the case that "A" and "B" are numerically the same in the actual world: criteria of identity and individuation. Those criteria vary as a function of the sorts of things that are at issue. Planets, persons, sports teams, cell lineages, ocean waves, etc., have different principles of individuation. Sometimes those principles mainly are matters of social convention but they can also be, in part, objects of scientific inquiry. — Pierre-Normand

Is there "right" and "wrong" criteria? Maybe one person is a scientist and says that the criteria for being water is its chemical composition, and so it doesn't make sense to say that in one possible world water is H₂O₂ , and another person is an architect and says that the criteria for being the Taj Mahal is its form, and so it makes sense to say that in one possible world the Taj Mahal is built from wood.

Maybe I'm like the latter and identify water by its appearance (which certainly would have been true before we knew about the periodic table). There's a possible world where H₂O₂ looks and tastes like water does in the actual world and which fills the oceans and falls from the sky as rain, so there's a possible world where water is H₂O₂.

That's not what I said. I said that perception is not identical to reality, which is what you said. — MindForged

OK, but that leaves me wondering how it was an objection? You also said:

We don't even have direct access to our own world, so are we able to learn anything about the actual world? — MindForged

This seems an attempt to give possible worlds the same epistemological status as the real world, hence my justification of direct epistemic access.

A consistent "set of facts" is one way of articulating what a possible world is so I don't even know what you think you're arguing against at this point. — MindForged

Facts are actual, not merely possible. Possible worlds might be a consistent set of posits, they are not a consistent set of facts.

Naturally "reliable" is doing all the work here, being used to obfuscate the fact that there's no guarantee that perception maps to reality such that we can have an infallible means by which to say some experience is reliable. It's like you've never considered any objection to your views ever. — MindForged

If I didn't consider objections, I wouldn't have said "reliable." Yes, it's doing a lot of work, but that doesn't mean that we can't have true knowledge, where "truth" is understood as adequacy, not as exhaustiveness or infallibility. I've made no claim of infallible human knowledge, so the notion of infallibility is a straw man -- effectively replacing human knowledge with divine omniscience. Primarily, "knowing" names an human activity, so requiring infallibility as you seem to is a bait and switch tactic.

Necessity is indeed defined as truth in all possible world [of the set of world being quantified over], and yes X being necessary entails that it's negation is not possible. Where is the circularity? — MindForged

If you can't see that using possible worlds as the ultimate basis for defining possibility is circular, I can't help you.

it's nonsense to say that "Venus" names the same object in every possible world because Venus does not exist in every possible world. — Dfpolis

This is exactly what I was talking about, you don't understand this topic. — MindForged

Thank goodness! I understand logic instead. Predicates predicated of multiple subjects are universals. Without equivocating, names can only be predicated of one individual. A "Venus" in another (possible) world is not our Venus. Therefore, one can only be call both "Venus" by equivocation or by universal predication.

But that's not how proper names work, they pick out a specific object in the actual world, and the meaning of that name is fixed in modal logic — MindForged

I am not disputing that the meaning of "Venus" is fixed. I'm asking that you look at how you fixed it. You told me that in each world where "Venus" designated, it designated the second planet from the sun. That is the definition of a universal. If you'd brought me out and pointed at Venus, and said "I call that thing 'Venus,'" you'd be giving it a proper name. But, when you say, "whenever there's a second planet, I'm calling it 'Venus,'" you're either defining universal term, or a set of homonymous names. If it is a set of homonymous names, you can't treat them univocally, which is what you're doing when you say the meaning is "fixed."

Now you say that I don't understand. Am I supposed to understand that the canons of logical predication do not apply to possible worlds? If so, on what factual basis? Surely it can't be because "Kripke has spoken"?

So, we come back to the definition from the SEP article: "A rigid designator designates the same object in all possible worlds in which that object exists and never designates anything else." The "same" of "same object" can't mean "identical" because if the Venus of a possible world were identically our Venus, that world would be identically our world. So, "same" must mean generically the same, not the identical individual. A term that designates generically similar objects univocally is a universal, not a proper name.

Obviously "Hesperus=Phosporus" isn't true in the possible worlds where the references to the terms do not exist. — MindForged

But, in my example, the terms are referential via the same types of experiences that give them reference here. Each rigid designator names is appropriate object: There are morning and evening stars and a second planet. It is just that the references are not what you want them to be. You response will define my possible world out of consideration. So, again, the conclusion is based on how you choose to construct a set of possible worlds, not on any observable facts of the matter -- and that is precisely my objection.

This is all consistent with Kripke's claim that proper names function as rigid designators, and also with his claim that statements of identity of the form "A is B", where "A" and "B" are proper names, are metaphysically necessary. — Pierre-Normand

It depends on how you define "metaphysically necessary." Can you define it without invoking possible worlds semantics? If not, how can this claim be relevant to reality?

speaking of worlds as simply "possible" allows one to confuse logical, physical and ontological possibility. — Dfpolis

...distinctions whose advocates can't specify what they mean by them — Michael Ossipoff

I can. I said :

"P is possible with respect to a set of facts, S, if P does not contradict the propositions expressing S." — Dfpolis

Logical possibility means the proposition is consistent with S = the facts we know.

Physical possibility means the proposition is consistent with S = the laws of nature.
Alternately, one may mean the proposition is consistent with S = the laws of nature plus the facts we know about a physical state.

Ontological or metaphysical possibility means the proposition is consistent with S = the nature of being qua being.

You are under the impression that a rigid designator is a term that could not have meant anything other than what it actually means. This is not what a rigid designator is. Rigid designation pertains to the meaning of a term as it actually is (or as it is in some single possible world). It is a contingent fact that a word is a rigid designator; and being a rigid designator means that it, in that contingent state of affairs, has the same denotation relative to all possible worlds.

You won't be able to mount a coherent criticism until you understand the subject. Read Naming and Necessity, or the article again more carefully.

A "Venus" in another (possible) world is not our Venus. Therefore, one can only be call both "Venus" by equivocation or by universal predication. — Dfpolis

There is, according to Kripke, no "second Venus" off in another world. To speak of Venus in another possible world is just to speak of Venus, that very same individual, as it might have been. You are imagining possible worlds as if they were foreign countries filled with distinct objects, but this is not what Kripke takes possible worlds to be. Again, read Naming and Necessity. Your objections are misinformed.

What makes it the case that one thing in one possible world and one thing in another possible world are the same thing? — Michael

This is a misunderstanding of the Kripkean position. According to Kripke, we can speak of the same individual in distinct possible worlds. This is just a way of talking about the very same individual in two possible scenarios, which is something we do all the time. There is thus no problem of 'trans-world identity,' since it makes no sense to ask, of two individuals we 'look at' in possible worlds, in virtue of what they are the same. We are already speaking of the same individual by stipulation, as it might have been in various scenarios. As Kripke says, it is not as if we are taking a telescope and viewing far-off places with different objects in them, and then deciding post hoc on criteria to say they are 'the same.' This is the position of David Lewis with his counterpart theory – that is one possible interpretation of possible worlds, but as with Lewis' modal realism, is not mainstream.

Then perhaps if we use a simpler example of an inanimate object. In another possible world the Taj Mahal was built using different materials, or at a different location, or with a different architecture. Does that make sense? Is it just a matter of stipulation that we consider them the same thing (or different things) in each possible world? — Michael

There is an interesting issue that arises here. When we talk about ways the world might have been (or possibly could have been), some features of the world as it might have been are foregrounded, while others are backgrounded, in accordance with the pragmatic point of the counterfactual albeit possible scenario being considered. It may be that possible world models for the semantics of modal statements obscure this pragmatic feature of talk of possibilities when possible worlds are reified with excessive determinacy. (This may be a reason why Lewis runs into problems that he seeks to eliminate through getting rid of backtracking conterfactuals when he analyses statements of causal dependence between events).

Consider the statement that an aircraft that has actually (and accidentally) collided with the Taj Mahal might possibly have avoided destruction if the Taj Mahal had been built 50 meter further to the West, or had been made out of a gaseous material rather than being made out of stone. We have no trouble evaluating those statements as true. While the historical location and/or material constitution of the Taj Mahal are being foregrounded, the issue of its identity are being backgrounded. This backgrounding of irrelevant features (i.e. irrelevant with respect to the pragmatic context of the consideration of the counterfactual scenarios) also allows for so called counterlegal counterfactual statements. (Counterlegal counterfactual statements are being discussed by Marc Lange in Natural Laws in Scientific Practice.)

In another context, we may inquire whether or not the Taj Mahal could, in the first place, have been built in the different location and still count (in accordance with our actual linguistic practices for naming functional artifacts of this sort) as the Taj Mahal. In that case, we may be picturing an alternate history where the builders of the actual Taj Mahal have settled for a different location, 50 meters to the West of the actual location, and inquire whether it's still numerically the same artifact that would have been built. In that case, it's the issued of the identity of the artifact that is being foregrounded. So, it may be senseless to ask the bare question whether a specification of a "world" in which the Taj Mahal has been built 50 meter further to the West than its actual location is or isn't a specification of a metaphysically possible world. Whether or not it is might be felicitously(*) taken to be a metaphysically possible world might depend on the pragmatic point of the question and hence on whether or not the issue of the identity of the Taj Mahal is meant to be foregrounded or backgrounded.

(*) I am using "felicitously" rather in the way @StreetlightX recommended in his recent thread.

You believe in an un-acknowledged and unsupported assumption that the physical world that we live in is the "actual", "existent", "physical" and "real" one, in some (unspecified) sense in which the infinitely-many other possibility-worlds aren't. — Michael Ossipoff

I do not deny the existence of other universes in a multiverse, or even independently. I am only saying that, as we are not in dynamic contact with them, they are epistemologically irrelevant.

I also note that there is a difference between knowing as awareness of present intelligibility, which is an act of intellect, and believing as a commitment to the truth of some proposition, which is an act of will.

there's no reasons to claim that they're "real" or "existent", whatever that would mean. — Michael Ossipoff

Anything that can act in any way exists. That is sufficient reason to think that things that act to inform me are real.

There's no reason to believe that your experience is other than such an abstract logical system. — Michael Ossipoff

Of course there is. The things I experience act on me and I am aware of their action on me. Abstract logical systems do not act on me in the same way.

If you claim that this physical world is more than the setting for the hypothetical logical system that is your experience-story, then in what respect to you think that this physical world is more than that. — Michael Ossipoff

Because mere hypotheticals can't act on anything.

Do you believe in unparsimonious brute-facts and unverfiable, unfalsifiable propositions? — Michael Ossipoff

No.

Which child, if either, am I in each world? Is it simply a matter of stipulation? Do we simply say that I’m one or the other (or neither)? — Michael

Precisely. It is a matter of how one constructs their possible worlds and then chooses to identify their components. As there is no reality involved, there can't be any facts of the matter.

It depends on how you define "same". Lewis's suggestion was that "same" doesn't meaningfully apply to someone or something in a different possibility world, It's a different world, necessarily with different (even if identical) things. — Michael Ossipoff

Exactly. Therefore, they can't have the same proper name, only homonymous proper names.

This seems an attempt to give possible worlds the same epistemological status as the real world, hence my justification of direct epistemic access. — Dfpolis

It was that, and hence my response regarding how you do not have direct epistemic access. If this access isn't infallible then there's no particularly superior access to your purported knowledge of the actual world over what is possible.

Facts are actual, not merely possible. Possible worlds might be a consistent set of posits, they are not a consistent set of facts.

Do you ever stick to what you say or do you change it on a dime when an objection surfaces? Here's what you said before:

Yes, I used "possible" -- not essentially, but to avoid circumlocution. So, here's the same definition restated: "P is possible with respect to a set of facts, S, if P does not contradict the propositions expressing S."

You yourself referred to facthood in your definition of what "possible" is, so there's no way you can object to me doing the same. That's ridiculous. You either contradicted yourself or you just can't use modal concepts in which case this is all silly.

If I didn't consider objections, I wouldn't have said "reliable." Yes, it's doing a lot of work, but that doesn't mean that we can't have true knowledge, where "truth" is understood as adequacy, not as exhaustiveness or infallibility. I've made no claim of infallible human knowledge, so the notion of infallibility is a straw man -- effectively replacing human knowledge with divine omniscience. Primarily, "knowing" names an human activity, so requiring infallibility as you seem to is a bait and switch tactic. — Dfpolis

It's not doing a lot of work, it's doing all the work. The reason why you required infallibility (whether you acknowledge it or not) is because your initial claim in the OP was this:

First, it is unnecessary. As we can have no epistemic access to any world but our own, actual world, anything we can learn, we can learn from the real world.

My point was that we don't have any better epistemic access to the actual world because of the limitations of perception. Without infallible means of accessing the states of affairs of the actual world, what we perceive to be the case can easily fail to be so. Whatever you mean by "direct access" is completely opaque, and so recourse to reliability here is equally so.

If you can't see that using possible worlds as the ultimate basis for defining possibility is circular, I can't help you. — Dfpolis

It seems you are incapable of actually defending your argument on the crucial points. Possible worlds as a means to give semantics for possibility is not circular. The only way you could claim that is because the word "possible" is part of the name of the concept. It does not appear in how possibility is defined. P is possible if it is not necessary that ~P; that is, P is possible if there is at least one world in which P is the case. There is no mention of possibility there, ergo the standard definitions of modal terms is not circular.

A "Venus" in another (possible) world is not our Venus. Therefore, one can only be call both "Venus" by equivocation or by universal predication. — Dfpolis

Seriously, this is asinine. Possible worlds are not (unless you're David Lewis) being posited as literal other worlds in the same sense as the actual world. It's right there in the name, there's only one actual world. Venus in another possible world is still Venus as it might have been, the individuation conditions return the same object (that's why the names are a rigid designator).

But, in my example, the terms are referential via the same types of experiences that give them reference here. Each rigid designator names is appropriate object: There are morning and evening stars and a second planet. It is just that the references are not what you want them to be. You response will define my possible world out of consideration. So, again, the conclusion is based on how you choose to construct a set of possible worlds, not on any observable facts of the matter -- and that is precisely my objection. — Dfpolis

"Second planet" and "morning/evening stars" are not proper names. They are properties which Venus has. They are definite descriptions, not names, therefore they aren't rigid designators (which is why their truth does not necessarily hold across worlds). So yes your worlds aren't considered because you're not necessarily talking about Venus by simply describing it with a generic property many objects might have. Rather, the identity holds across worlds (i.e. trans-world identity) because they have the same essential properties which make it Venus. It's really no different than analyzing "Steve, you would have felt the warm air had you gone outside" as talking about the same Steve even if it's a counterfactual (Steve, by assumption, did not go outside).

We are already speaking of the same individual by stipulation, as it might have been in various scenarios. — Snakes Alive

That it's a matter of stipulation is an answer I posed to my own question.

But then that makes the notion of rigid designators philosophically uninteresting. I simply stipulate that in one possible world this glass of water is composed of H₂O₂ (and perhaps also that the Taj Mahal is made of wood), and so I've declared Kripke's claim that water is necessarily H₂O to be wrong (and then he's stipulated something else and so declared his claim correct).

It depends on how you define "metaphysically necessary." Can you define it without invoking possible worlds semantics? If not, how can this claim be relevant to reality? — Dfpolis

Saying that something is metaphysically possible just is to say that it isn't inconsistent with the way things can be in accordance with the constitutive rules that govern how those things fall under concepts. (For instance, it is a constitutive rule of bishops, in chess, that such pieces only moves legally along diagonals; and it is a constitutive rule of the concept of a human being that it is an animal). A state of affairs is metaphysically necessary if its non-obtaining (or the negation of the statement that it obtains) isn't metaphysically possible. Under that definition, I think it can be shown that if "A" and "B" are meant to function in the way ordinary proper names are used, and they both actually name the same individual, then it is metaphysically necessary that A and B are numerically identical.

You are under the impression that a rigid designator is a term that could not have meant anything other than what it actually means. — Snakes Alive

No, I am not under that impression. I think all terms are conventional. Only ideas cannot mean anything but what they mean, because their whole being is meaning what they signify.

That seems wildly incomparable. If I say "You would have enjoyed yourself had you gone to the party", the "you" there (assume it means Michael) is stipulated to be the same object and a posited truth had you done something else. There doesn't seem to be any issue to most people in doing this. The Taj Mahal being made of something else would cause it to have a different identity and so it couldn't be reasonably posited as being the same object.

But then that makes the notion of rigid designators philosophically uninteresting. I simply stipulate that in one possible world the Taj Mahal is made of wood and that this glass of water is composed of H2O2, and so I've declared Kripke's claim that water is necessarily H2O to be wrong (and then he's stipulated something else and so declared his claim correct). — Michael

If water is H20, it makes no sense to 'stipulate' that a glass of water does not hold H20. Perhaps 'water' doesn't really mean the same as 'H20' – probably, it does not.

All this has nothing to do with the force of Kripke's arguments that names are rigid designators, and not disguised predicates of some sort.

My point is not that you think this, but that you think that Kripke does. In other words, you are confused about what the technical term "rigid designator" means.

If water is H20, it makes no sense to 'stipulate' that a glass of water doe snot hold H20. — Snakes Alive

And if the Taj Mahal is made of bricks then it makes no sense to stipulate that in a possible world it's made of wood? Or if my name is Michael then it makes no sense to stipulate that in a possible world my name is Andrew?

And if the Taj Mahal is made of bricks then it makes no sense to stipulate that in a possible world it's made of wood? Or if my name is Michael then it makes no sense to stipulate that in a possible world my name is Andrew? — Michael

No, it is perfectly possible to stipulate that an individual may have had some properties other than what it has (being made of something different, or having a different name).

What makes less sense is to stipulate that one object is identical to another in some other possible world. If 'water' means the same as 'H20,' the idea is that you could not refute this by stipulating that a glass of water held H202. H202, you will note, is not water, but hydrogen peroxide.

No, it is perfectly possible to stipulate that an individual may have had some properties other than what it has (being made of something different, or having a different name). — Snakes Alive

And in my case the individual is "this glass of water" and the counterfactual property is the chemical composition.

If 'water' means the same as 'H20'

Well that's what I'm calling into question. I might counter by saying that the term "water" refers to whatever liquid makes up the Earth's oceans and falls from the clouds as rain and that in some possible world the chemical composition of that liquid is H₂O₂. That water is H₂O is just a contingent fact about the actual world, much like Earth being the third rock from the Sun.

H202, you will note, is not water, but hydrogen peroxide.

So I'm saying that in one possible world water is hydrogen peroxide.

Well that's what I'm calling into question. I might counter by saying that the term "water" refers to whatever liquid makes up the Earth's oceans and falls from the clouds as rain and that in some possible world the chemical composition of that liquid is H2O2. That water is H2O is just a contingent fact about the actual world, much like Earth being the third rock from the Sun. — Michael

In that case you are using the term "water" to refer to a general definition and hence what you are saying about water, and possibles worlds in which water had alternative chemical constitutions, doesn't really have any bearing on what Kripke (and Putnam) have said about the the semantic properties of natural kind terms, or the metaphysics of natural kinds. It is natural kind terms, and not general descriptive concepts, that are deemed by Kripke to function as rigid designators. (Putnam has further shown how this thesis dovetails with semantic externalism).

And in my case the individual is "this glass of water" and the counterfactual property is the chemical composition. — Michael

Then what you are supposing is that the glass of water had instead been a glass of hydrogen peroxide.

Well that's what I'm calling into question. I might counter by saying that the term "water" refers to whatever liquid makes up the Earth's oceans and falls from the clouds as rain and that in some possible world the chemical composition of that liquid is H2O2. That water is H2O is just a contingent fact about the actual world, much like Earth being the third rock from the Sun. — Michael

Whether 'water' really means the same as 'h20' is debatable, and I think probably false. But this was just a stock example Kripke used, so too much importance shouldn't be placed on it. It would be better to pick an example you agree on, and use that. Kripke's claim is that both expressions are to be taken as naming a certain kind of thing, and not offering a description of some sort, whose exemplifier might vary from world to world.

In fact, your suggestion doesn't disambiguate between these two possibilities. Of course water is the substance that fills the oceans, etc. Does that mean that the word 'water' means the same as 'the substance that fills the oceans...', etc. No, obviously these do not mean the same, since it is no contradiction to imagine instead that the oceans had been filled with mercury, and in doing so we are imagining a different sate of affairs, a way things could have been, but aren't.

That said, we might say that what water is is just that stuff, and to get an idea of what we mean by
'that stuff,' we say, the stuff that actually fills the oceans, etc. right now. Then by water we still mean just that substance, and the term rigidly designates that substance. But we used a description in the actual world to give people an idea of which substance we meant.

So I'm saying that in one possible world water is hydrogen peroxide. — Michael

I must confess, to me this sounds like a contradiction, and I do not know how to suppose such a thing – it is like supposing that 2 and 3 make 6, or something like that. If it were hydrogen peroxide, well then, it would be hydrogen peroxide, not water.

Of course, you can imagine a world in which hydrogen peroxide falls from the sky, and fills the oceans, and people drink it, and in which it therefore plays a similar role as the role played by water actually. But then, you are not imagining a world in which water does these things, but in which hydrogen peroxide does, which is something different. Perhaps by 'water is hydrogen peroxide,' you are speaking metaphorically, and mean only that hydrogen peroxide fills the same role as water does actually. But taken literally, it is a difficult claim to make sense of.

Then what you are supposing is that the glass of water had instead been a glass of hydrogen peroxide. — Snakes Alive

No, because I'm stipulating that it's the same glass of water. It's just that in the actual world it's H₂O and in a possible world it's H₂O₂.

How is this any different to stipulating that I'm married to the same woman, but that in the actual world she's English and in a possible world she's American?

In fact, your suggestion doesn't disambiguate between these two possibilities. Of course water is the substance that fills the oceans, etc. Does that mean that the word 'water' means the same as 'the substance that fills the oceans...', etc. No, obviously these do not mean the same, since it is no contradiction to imagine instead that the oceans had been filled with mercury, and in doing so we are imagining a different sate of affairs, a way things could have been, but aren't.

It's also no contradiction to imagine that scientists have been mistaken (or lying) and that the chemical composition of water in the actual world really is H₂O₂.

I must confess, to me this sounds like a contradiction, and I do not know how to suppose such a thing – it is like supposing that 2 and 3 make 6, or something like that. If it were hydrogen peroxide, well then, it would be hydrogen peroxide, not water.

Things can have more than one name. The liquid we drink can either be called "water" (a common name) or "hydrogen peroxide" (a scientific name, referring to its chemical composition), so water and hydrogen peroxide are the same thing, and H₂O is something else. This might be false, but it's not a contradiction.

You said:

Facts are actual, not merely possible

But you don't know what you mean by "actual". Or, if you do know what you mean by it, you're keeping it to yourself.

Possible worlds might be a consistent set of posits, they are not a consistent set of facts

[/quote]

You see, that's where you're wrong.

There are infinitely-many completely hypothetical worlds and stories that consist of consistent sets of facts. I spoke of hypothetical life-experience stories that consist of complex systems of inter-referring abstract implications about hypothetical propositions about hypothetical things, and the many consistent configurations of mutually-consistent hypothetical truth-values for those hypothetical propositions.

Those abstract implications that I referred to above are facts.

An implication is an implying.

In logic usage, it's an implying of one proposition by another proposition.

"Fact" is often or usually defined as a relation among things, or as a state-of-affairs.

An implying of one proposition by another proposition fits both of those definitions.

But we needn't quibble about what you think "fact" means. I said what I meant without using that word. The question was, in what regard, in what manner, do you think this physical world is different from merely the setting for your hypothetical life-experience-story, consisting of a hypothetical logical system such as I've described?

Regarding your other posted answers, I'll reply to them tomorrow morning.

I just wanted to correct your above-quoted statement in this post today.

Michael Ossipoff