Well, "it is possible" does pertain to the future, because it is in the future that the possibility resolves. If it is possible that I win the race, I win or lose the race in the future. Past possibilities - "it was possible" - are, by implication resolved and I have already won or lost. I do think that, like probabilities, the future is part of the concept. — Ludwig V

Modal statements can be made about the past present and future. Possibility entails contingency. We typically regard future facts as contingent - there is a set of possible outcomes. A present state of affairs may also be contingent: consider where you live today - it's a fact that is contingent upon a past choice, from among a set of possibilities.

It is tempting to agree that counter-factual is a possibility. But the game of alternative history suggests that a counterfactual does not contemplate a possibility, but an event, whether it is possible or not. "How would things be now if Hitler had won the war?" Since he did not, it is not possible that he did. Yet somehow we can contemplate that eventuality and build a coherent story from it. — Ludwig V

The counterfactual COULD be a possibility - if what actually occurred was contingent. This would mean that there was something about the past event that could have been different. If no relevant fact could have differed, then what occurred was necessary.

Regarding Hitler: some have suggested that if Germany had developed the Atom Bomb earlier, then Hitler would have won the war. Was the timing of their research truly contingent? Maybe not, but that is the way to think about it.

Here's what seems to be a truly contingent fact: the precise time at which a beta-decay occurs - the time at which the nucleus of an atom emits a beta particle. The exact time is due to quantum uncertainty. If the clock could be rewound. perhaps the time of the decay would differ.

Since he did not, it is not possible that he did — Ludwig V

This conflates possibility with potential. It's true that, given what occurred, the counterfactual is not possible. But the question is whether or not what occurred was necessary or contingent.

the inferences are all qualified by, "within Tolkien's fictional world...".
— Relativist

Yep - treating it as a possible world, and truth as true-in-a-world. — Banno

So....treating it as a possible world, even though it's not possible.

"unqualified" is problematic; we can take this world, the one we are in, to be w₀ and then define truth simpliciter as true-in-w₀. And note thatin w₀ it is true that in Tolkien's world Frodo is a hobbit... — Banno

Doing what you suggest is inconsistent with correspondence theory of truth - the Frodo statement is not "true" under this theory. You may have a different theory of truth, but we can each draw the same inference. I would retain the context: it is true that in Tolkien's fictional world, that Frodo is a hobbit.

And critically- nothing here establishes the hobbit world (in toto) as anything more than a fiction, so calling it a "possible world" is misleading.
— Relativist
Yes. This is a different point, further complicating the issue. — Banno

On the contrary: it is more straightforward, certainly for anyone who accepts correspondence theory (like the majority of philosophers).

in the actual world Tolkien developed Frodo as a fictional character, we might decide that Frodo is necessarily a fiction ....

It would require some analysis to make the case that it is necessarily a fiction. The same analysis is appropriate for any so-called "possible world": we want to make the judgement as to whether a "world" is possible, necessary, or impossible. Even a metaphysically impossible world could be internally coherent.

the existence of the book does establish that there is a fictional world — Ludwig V

Yes, but the same could be said for any so-called "possible" world one entertains with the semantics. If I had my way, we'd distinguish between fictional and possible worlds.

I agree that there is this difference between a fictional world and a possible world, that the possible world might or might not exist - become actual, if you will... — Ludwig V

Only if it pertains to the future, and is consistent with the history of the world up to the present, and everything else we know about the world.

However, when entertaining counterfactuals about the past or present, the implication is that this counterfactual world could possibly have happened. But could it? This is analyzable and debatable. It's a very different debate if we're simply examining the coherency of a fictional world.

Regarding plausibility: that just seems an epistemically weaker form of possible, and could apply to either fictional and (truly) possible worlds. Perhaps it's equivalent to epistemic possibility: as far as I know (implicitly based on my internalized beliefs), it is possible.

Another way to ask this: what is it that establishes the truth of the statement, "there is a possible world in which Hobbits, Trolls and Orcs exist"
— Relativist
Why isn't a copy of the book(s) enough? — Ludwig V

The book establishes a fiction. We could examine this fictional world for coherence, and draw valid inferences if (and only if) it is, but the inferences are all qualified by, "within Tolkien's fictional world...". But no unqualified objective truths can be inferred.

And critically- nothing here establishes the hobbit world (in toto) as anything more than a fiction, so calling it a "possible world" is misleading.

That, I believe is why concretism is unacceptable. We produce a fictional idea, a possibility, then to make it fit within the possible worlds semantics, we assign concrete existence to it. This is unacceptable, to arbitrarily, or for that stated purpose, assign concrete existence to something completely imaginary. It demonstrates quite clearly the deficiency of possible worlds semantics. To conform we must accept what is unacceptable. — Metaphysician Undercover

There's a lot you and I disagree about, but I 100% agree on what you said here.

The truth of a possibility in language can only be established using a coherence theory...

Therefore, if we can coherently talk about the possibility of Hobbits, Trolls and Orcs, which we can, then this is sufficient to ensure the truth or falsity of our statements. — RussellA

Thanks for the clarification, but it provides a good reason for many of us to reject it - since it depends on coherence theory of truth. Obvious objections:

"May not a paranoid's delusions of persecution be frighteningly coherent? May not a patient's faith that a mere placebo is a wonder drug be therapeutically useful? Russell was quick to claim in opposition to Joachim that multiple systems of beliefs may be internally consistent, though incompatible with each other. Nietzsche had already suggested well before James that false beliefs may be not merely useful but indispensable for life. "
--Truth -PRINCETON FOUNDATIONS OF CONTEMPORARY PHILOSOPHY ; Burgess & Burgess, pg 3

Kripke had a more nuanced theory, but it strikes me as a move to rationalize possible world analysis.

At any rate, anyone who chooses to take possible world analysis seriously ought to understand the dependency on coherence theory of truth.

I think I understand where you're coming from, but my attempts to get people to understand where I'm coming from haven't gotten traction. I'll start a new thread with my issues, and let you carry on here.

But again, it's not My brand of modal sophistry. It's the standard, accepted logic of modality. — Banno

I think you're alluding to modal logic as a formal system. One can utilize the formal system to go through the mechanics of the logic, without committing to possibilism/actualism much less necessitarianism/contingentarianism.

I can imagine a possible world that is as concrete as ours, where the Hobbits, Trolls and Orcs that inhabit this world believe themselves as real as we believe ourselves. — RussellA

What would make such a world POSSIBLE? IOW, how do you account for its existence?

Another way to ask this: what is it that establishes the truth of the statement, "there is a possible world in which Hobbits, Trolls and Orcs exist"?

This cannot be correct. If each possible world is separate from every other, in an absolute sense, then there would be no point to considering them, as they'd be completely irrelevant.
— Metaphysician Undercover

For Lewis’ Concretism, these possible worlds are concrete worlds — RussellA

If there is no causal connection sometime in history, in what sense are they possible?

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

Contradictory propositions cannot both be true 'at the same time and in the same sense. I was responding to your statement that the propositions needed context. I was pointing out that modality is also relevant.

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. — RussellA

It doesn't require believing in determinism, it depends on believing only that the rising of the sun is a consequence of deterministic laws of nature, and that the prior history of the universe is a given (a history that may include contingent events).

The conservative publication, The National Review, wrote this about the President:

"The president of the United States is a hateful raging lunatic with all the empathy of Jeffrey Dahmer....

"This president cannot discern moral right and wrong through a person’s actions, like a normal human being. Donald Trump’s entire worldview of whether someone is a good person or a bad person depends entirely on whether that person offers praise or criticism of Trump....

"The guy who can’t feel empathy for the Reiners being stabbed to death by their son is also not going to feel empathy for the people who contend the cost of living is still high, which is why the president keeps running around insisting the word “affordability” is a Democratic hoax and that Americans are living in a “golden age.” "

https://www.nationalreview.com/the-morning-jolt/trumps-appalling-reiner-reaction-is-a-sign-of-something-deeply-wrong/?fbclid=IwdGRjcAOy-9NjbGNrA7L7x2V4dG4DYWVtAjExAHNydGMGYXBwX2lkDDM1MDY4NTUzMTcyOAABHnJxOyFQAVCJjX1dmES254hLB4rSz1E_i8Pfr0KYkMaO-4rPyHy5KoAfFzrN_aem_Z3LmBDa7udmeucM2zYEPgg

I see what you mean. Thanks for explaining.

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.

Please explain what you think I got wrong.

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.

Equating the “actual world” of a model with an ontologically privileged world is a misunderstanding. Modal logic does not commit to idealism or deny the existence of the external, physical world; it merely provides a framework for reasoning about possibility and necessity. The indexical nature of “actual” dissolves the apparent problem: there is exactly one designated actual world in the model, but this says nothing about reality beyond the model. — Banno

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

Possibilists claim that we can: we must simply broaden our understanding of reality, of what there is in the broadest sense, beyond the actual, beyond what actually exists, so that it also includes the merely possible. In particular, says the possibilist, there are merely possible people, things that are not, in fact, people but which could have been. So, for the possibilist, (4) is true after all so long as we acknowledge that reality also includes possibilia, things that are not in fact actual but which could have been; things that do not in fact exist alongside us in the concrete world but which could have. Actualism is (at the least) the denial of possibilism; to be an actualist is to deny that there are any possibilia. Put another way, for the actualist, there is no realm of reality, or being, beyond actual existence; to be is to exist, and to exist is to be actual. In this article, we will investigate the origins and nature of the debate between possibilists and actualists.

That article has a link to a supplement that outlines Lewis' view: Classical Possibilism and Lewisian Possibilism. The first thesis of the outline is:There is a plurality (indeed, a plenitude) of worlds.. So when you refer to indexicality, among these worlds - it is in the context of this thesis.

This supplementary article goes on to say:"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. "

This seems to suggest that each world within the "plenitude of worlds" has a similar status, and it seems to me this status entails existing. (There is a plenitude of worlds uses "is" - a form of the verb, "to be" = existing).

If this discussion were solely about interpreting Lewis, it would be reasonable to stay within his framework and terminology. But the context is broader, so we shouldn't need to limit ourselves to it. Most of us believe the world we live in is the only actual world, irrespective of Lewis' view and his terminology. Any hypothetical world other than this one is, at best, a possible world.

My issues have been:
1) possibility can be expressed in a variety of modalities, and when we don't specify that modality, confusion is likely to occur.
2) it is debatable as to whether any of the non-actual "possible" worlds are metaphysically possible. I suspect they are only epistemically possible (i.e. they only seem possible because of our limited knowledge).

The point, though was that all the possible worlds are actual worlds. If we say "possible" that means "may" be. But Lewis' interpretation appears to be that each possible world "is" an actual world. That's what we were discussing, all the possible worlds are actual worlds. — Metaphysician Undercover

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.

Contingent" has varied meaning, it's quite ambiguous. — Metaphysician Undercover

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.

The words actual and possible are still needed.

In conversation, I might say “the sun might not be shining”, but would be confusing to a listener as it lacks context. It would be better to say “it is possible that the sun might not be shining”, as this does infer a context.

Similarly, my saying “the sun is shining” lacks context. It would be better to say “the sun is actually shining”.

The words "possible" and "actual" add context. — RussellA

The modality is equally relevant. Your modality is epistemic: given the facts available to you, it is (epistemically) possible the sun is shining.

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).

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

Kripke’s Theory of Naming thereby avoids any philosophical problems with the ontological nature of essence or identity. — RussellA

That was one of my points. Particularly in the context of this thread, which (per the 2nd article in the Op) IS about the ontological nature of possibility. Transworld identity is pertinent to that.

That sounds reasonable. I stand corrected.

If information can exist in the presence or absence of consciousness... — Patterner

That was part of my point: information does not exist in the absence of (an aspect of) consciousness. Characters on a printed page are not intrinsically information; it's only information to a a conscious mind that interprets it- so it's a relational property.

If a walking robot with a mechanical eye is approaching a cliff, and turns to avoid it, was it because there was information? — Patterner

Of course, and I agree information is relevant to ongoing mental activity. What I was referring to was understanding the fundamental nature of consciousness - the hardware that produces it. I should have been more clear. Sorry.

consciousness is best understood in terms of information — hypericin

What is information, in the absence of consciousness? Words on a page have to be interpreted by a conscious mind.

I'm fine with examining aspects of mental activity in terms of information, but information needs to be grounded in something else, to avoid circularity.

Kripke's defining of "rigid designators" is useful for identifying posteriori necessity (It is a necessary fact that Hesperus is Phosphorus), but it falls short when applying it to possible worlds.

You refer to Kripke's "necessity of origin". Kripke writes:

"How could a person originating from different parents, from a totally different sperm and egg, be this very woman? One can imagine, given the woman, that various things in her life could have changed...One is given, let's say, a previous history of the world up to a certain time, and from that time it diverges considerable from the actual course...And so it's possible that even though she were born of these parents she never became queen...But what's harder to imagine is her being born of different parents. It seems to me that anything coming from a different origin would not be this object" - Naming and Necessity, p 113

So he's saying an individual is essentially tied to particular features of its origin in a way that it is not essentially tied to particular features of its subsequent history. Further, he's saying that origin is a necessary condition, not a necessary and sufficient condition. Here's what he has to say about identity over time:

"adequate necessary and sufficient conditions for identity which do not beg the question are very rare...Mathematics is the only case I really know of where they are given within a possible world. I don't know of such conditions for identity of material objects over time, or for people. Everyone knows what a problem this is. But let's forget about that." -Naming and Necessity p43

If he can't account for identity over time, then he can't account for true trans-world identity either. Both would require sharp criteria that are both necessary and sufficient. Kripke is just suggesting some rules for the game of entertaining counterfactual worlds. They're OK rules, although different views of what is essential to an identity could lead to different rules.The issue is that the rules do not entail that these counterfactual worlds are actually POSSIBLE.

So some of us object to labeling them "possible worlds" because they are fictions with some things in common with the actual world without regard to whether these fictions could have occurred. This is purely a semantics issue. But the more serious issue is that Kripke gives very little insight to (The Possibilism-Actualism debate).

As the Wikipedia article says, the possibilist believes "There are possibilia, that is, things that are not actual but could have been." It's an ontological debate, that Kripke doesn't participate in.

Sure, all physical things and actions can be understood as "contingent". That means their existence is dependent on causation. — Metaphysician Undercover

No, that's not what contingent means. Suppose necessitarianism is true. Necessitarianism is the theory that every that event that occurs (past and future) occurred necessarily. IOW there are contingent events and no objects that exists contingently.

Under this theory, laws of nature necessitate their result. Where A and B are states of affairs, if A causes B, through a law of nature, then A necessarily causes B. If you have a ball in your hand, and you release the ball, it will necessarily fall to the ground (assuming there is nothing in the environment to impede the fall). Classical laws of nature work like this.

Contrast this with a quantum event, whose outcome is a consequence of quantum uncertainty. The specific result was not necessary (under most interpretations of QM). It was contingent. And yet, it was caused. So causation can either produce its effect necessarily or contingently. It becomes a historical fact that the effect was contingent vs necessary.

Unfortunately your definition of contingency mixes causality and and modality. If it were a definition of determinacy, it would work. — Banno

I wasn't "defining" possibility, I was discussing the ontology of possibilty - pertinent to the discussion of
"The Possibilism-Actualism Debate", referenced in the Op.

There are no metaphysically possible worlds unless there is contingency in the world, and this implies an ontological basis. You aren't obligated to participate in discussing that, but it is erroneous to suggest it's not a legitimate issue that directly relates to the topic.

For those reading along, the standard definition of contingency is roughly just that an event is contingent if it is true in some but not all possible worlds.

This has the great advantage of not involving any notion of causality or temporality. — Banno

IOW, it ignores the controversies. I have inferred that the controversies are the topic of this theead.

when we look to the past and say that Y could have occurred instead of X, this is to project the present into the past, and say that at that time, when that was present, Y could have occurred. But this is a fictitious projection of the present back into the past, which is really not possible to do, go back in time. — Metaphysician Undercover

You're conflating possibility with potential. There is no potential for a different past, but we can consider whether a past event was necessary or contingent.
The past event E was contingent if the causal factors (C) that produced E had the potential (at the time) to produce E or ~E. IOW, both E and ~E were possible.

After the event, it will remain a historical fact that E was contingent (E and ~E were possible).

Of course fuzzy logic is algorithmic to some degree or it wouldn't be programmable for digital computers. But it's much more flexible & adaptable to the non-algorithmic real world than sharp line-item programming — Gnomon

You're presuming that "real world" human reasoning is somehow beyond duplicating. I don't see any problems at all, because any specific issue you might bring up could be dealt in the design- either in software or hardware. If digital computing seems too "sharp"- analogue computing could be used. However, there really isn't anything an analogue computer can do that couldn't be implemented in software. For example, Artificial Neural Networks engage in the analog process of pattern recognition - and yet, the underlying technology is digital processing.

self-awareness seems to require something a bit beyond just fuzzing the focus : a generalized contextual worldview and an embodied subject. :smile: — Gnomon

Three issues:
1) The thought processes involved with much human reasoning do not seem to require self-awareness.
2) For a thought process in which self-awareness was a factor, the role that it plays could be simulated.
3) If the feelings issue could be solved - it might actually be possible to induce true self-awareness (this is my theory).

Yes. Non-algorithmic Fuzzy Logic*1 is an attempt to make digital computers think more like humans. And it may be necessary for Chat Bots to deal with imprecise human dialog. Yet it reduces the primary advantage of computers : precision & predictability. — Gnomon

Fuzzy logic and paraconsistent logic ARE algorithmic- it's feasible to program these. The programmming could keep it predictable (a given input will necessarily produce the same output), or randomness could be introduced.

Neither of these processes is inconsistent with standard 1st order logic. Standard logic is a special case of fuzzy logic with each premise assigned a 100% certainty.

Microprocessor inventor, Federico Faggin says : "There is an unbridgeable gap between artificial and human intelligence, which is characterized by comprehension : a non-algorithmic property of consciousness that is often underestimated and inaccessible to computers" — Gnomon

He is expressing an opinion, one that I regard as rooted in a lack of imagination.

To be clear (and to repeat what I've said elsewhere in this thread), feelings are not algorithmic. They are the one serious challenge for physicalism. They do not, however, falsify it.

Set that challenge aside for the moment, and assume as a premise that feelings could be added to the hardware. I suggest that this would make it feasible to duplicate human reasoning: not a mere simulation, but duplicating the algorthmic processing that it involves.

At the present, looking forward in time, we have real ontological possibilities in relation to what may occur, and this affects our decisions on actions. In this case, "possible worlds" might be acceptable. If we believe in free will, rather than determinism, the possible worlds of the future can have real ontological status, as real possibilities. — Metaphysician Undercover

We seem to be on similar tracks, so far. But I'll expand on this.

If determinism is true, then there is actually only one future possibility: the actual world that will unfold to us. Of course, we're ignorant of the future (except to the degree that we can apply the laws of physics). On the basis of this ignorance, we can discuss epistemic possibilities- as far as I know X (a future event) is possible.

As you said, if (libertarian) free will exists, then there are multiple (metaphysically) possibly futures. Further, quantum indeterminacy establishes multiple (physically) possible futures.

At the present, looking backward in time, there is no ontological possibility in relation to what has happened. The past is fixed, and presents us with what actually is, as we understand the empirical observations which have occurred. — Metaphysician Undercover

However, if determinism is not true then there were past contingencies: events in which X occurred, but Y could have occurred instead. This could make it reasonable to consider possible worlds in which those past contingencies were realized. But this only opens up only limited possibilities.

And at the present there is ontological possibility toward the future, so we can talk about what could have happened if things had played out differently, when 1972 was the active present. This is fictional, because we cannot actually put the present back in time, to play things out differently. So this ought not be represented as "possible worlds", to distinguish it from real possible worlds looking forward in time. And we have a goof name for that "counterfactual" so we might call it counterfactual worlds. — Metaphysician Undercover

If voters exercised LFW, then perhaps a different outcome could have occurred- but even LFW choices are made for reasons that would still be present- so it's too far-fetched to take seriously.

"Counterfactual fictions" would be a more precise label for discussing the past.

I agree with pretty much everything else you said.

Again, that is the cart before the horse. For Kripke Essence is a consequence, not a beginning. — Banno

The reasoning is inescapably circular!

It starts with the assumption an object is the same object in a (non-actual) possible world (it has a trans-world identity) and then conclude that the object must have an essence that accounts for it being the same object.

What you fail to grasp is that trans-world identity is controversial. Kripke does not solve the contoversy- he just alligns to one side of it.

I read Naming and Necessity some years ago. Later, I read Mackie's How Things Might Have Been*. The latter was written after Kripke's work; she references Kripke, Lewis, Plantinga, and others - and demonstrates the problems I have been relating to you. Responding, "but Kripke said...." is not a refutation.

*Mackie also wrote the SEP article on Transworld identity. The article summarizes the arguments in her book. I recommend you read it.

the claim that “Kripke’s theory of possible worlds is contingent on essentialism being true” gets the explanatory order wrong. Essence is explained in terms of necessity, not necessity in terms of essence. — Banno

The "explanatory order" doesn't falsify the logic: there's s logical dependency on essentialism. But go ahead and explain essence.

The opposite extreme: 100% of an objects properties (all of which are qualitative) at time t1 are necessary and sufficient for being that object at t1. This is my view.
— Relativist

That is my view too — Metaphysician Undercover

The implication is that there is only one possible world: the actual one. Do you agree?

When we conceive of (allegedly) possible worlds, we are constucting a fiction. IMO, the semantic framework can be useful for analyzing possibilities, but the exercise should not be taken too seriously.

Kripke was an essentialist: he believed individual identity was associated with its essence - a subset of an individual's properties.

So his theory of possible worlds is contingent upon essentialism being true. It falls apart if essentialism is false. My position has been that it is false. Can you defend essentialism?

You have not addressed what it means to be the "same" individual. You simply assume it's the same. That creates a logical contradiction under my definition of individual identity.

You can disagree with my definition, but then you need to provide your own.

Relativist: A rigid designator refers to a specific individual in this world. '

A rigid designator refers to the very same individual in every world in which it exists. — Banno

Under my view of individual identity, that is logically impossible.

My view is that 100% of an individual's properties (including intrinsic properties and relations to other objects) at each point in time, are necessary to being that individual.

This is what you aren't addressing.

In Kripke's system, and in the example we just gave, Prince Charles is imposed, fixed by the act of rigidly designation, and it's this very supposition that sets out that the Prince Charles in the alternative possible world is exactly the same Prince Charles as is in the actual world. — Banno

A rigid designator refers to a specific individual in this world: he has a specific physical composition at each temporal point of his existence, a specific history, and a set of relations to every other object in the universe. If we mentally place the individual in another environment, some of those relations are dropped. Since the world is different, he may have a different history - this may result in differences in his physical structure, and his memories. The more different the world, the more differences from the real world.

So it is never the case that it is "exactly the same individual" because there are necessarily differences. You have to designate what properties and relations make it "the same".

In Lewis' system, there is an algorithm to decide which person in some other possible world is the counterpart of Prince Charles. — Banno

Counterparts do not have the same identity as the person being discussed. It's perfectly fine to reference counterparts- individuals with similarities to the one referenced.

Transworld identity or counterpart theory is not discovered by the model, it is presupposed — Banno

Which makes it fine for an intellectual exercise, but it does not establish possibilia: that the "possible world" being analyzed is possible.

What I mean by "possible" is that it is metaphysically possible: the "possible" world would have been the actual world, had certain continencies occurred. Just because we can conceptualize a world does not imply it was metaphysically possible.

can True/False computers replace Maybe/Maybe-Not human philosophers?* — Gnomon

Fuzzy logic and paraconsistent logic address this, at least to a degree.

We ask "What if Prince Philip had passed before his mother?" and understand that this is about sentences about Prince Philip and Queen Elisabeth, and we do that without the need for the philosophical baggage of haecceity. — Banno

Of course, we can entertain any conceivable "what-if?", but entertaining it does not entail that it was truly possible.

Trans-world identity is closely related to identity over time: what is it that makes any object the SAME object from one day to the next? Is there a subset of the object's properties that are necessary and sufficient? Imagine a big rock that is eroding over time: is it the same rock when it's 5 kg? 2 kg? 1 gram?

Similarly, with people: are you the same person as the infant that grew and developed into you? We naturally assume so, but analyze it: what makes both of them the same person? DNA mutates over time; your dimensions change; you gain memories, physical scars, etc. There's no set of necessary and sufficient properties that comprise the essence* of you. Rather: you have a causal relation with each prior version of you: Thursday-you is a material cause of Friday-you. There's also a continual piling on of new memories.

This is how I suggest we have an identity over time- but it means these hypothetical thought experiments are not really referring to the same identity. Actual Queen Elisabeth had a very specific history, and it is that history that strictly defines her identity.

There's also a matter of how the counterfactual situation would have come about: Elisabeth and Philip died when they did for some very specific reasons. So for the counterfactual to be truly possible, one or more of those reasons would have to have differed. For it to be truly possible, there needs to have been some contingent factors. If determinism is true, then there is no contingency.

_________
*haeccity, if it exists, would be the essence of a identity.