Well, you don't have to be on this thread. What do you want?

All I want is open and reasonable discussion. I don't see the relevance of such counterfactuals as "Janus might have been wearing red shoes" for considerations of how identity might be established and the role of genetics in determining identity, which is what I thought this thread to be about.

You don't see the relevance of counterfactuals to questions of possibility and necessity. Ok, then.

I gather this doesn't help... Counterfactuals?

I don't see a way to proceed until you express whatever it is you are supposing.

You don't see the relevance of counterfactuals to questions of possibility and necessity. Ok, then.

I gather this doesn't help... Counterfactuals? — Banno

The problem I have is that we cannot know if the possibilities we can imagine are actual possibilities or merely logical possibilities. It doesn't seem that hard to determine what can be coherently imagined; that is we can coherently imagine whatever is not self-contradictory.

When I have some more time, I'll read the article you linked; then I guess I'll find out if it helps me to see that counterfactuals have relevance beyond just what we are able to coherently imagine, or if it cements the intuition I already hold.

I'll read the article you linked — Janus

Ok.

Oh, this is an actual question about another poster?

No I am not him. Why did you think that? Never heard of that name until I looked it up just now.

K1 is invalid. Kripke justifies its occasional use as “by a priori philosophical analysis”... a somewhat ambiguous phrasing. — Banno

That's very interesting. So many questions. I used to accept it before I read Naming and Necessity but that article persuaded me that it's meaning, if any, is extremely obscure. One day, perhaps, I will be able to cross-question you.

The example from (1971) is that this wooden lectern could not have been made of ice, because then it would not have been this lectern... it would have been a different lectern. — Banno

Yes. I was entranced, reading that passage, by the rhetorical gestures that Kripke felt he had to resort to in explaining his meaning; one could almost hear him thumping it. It isn't quite clear to me why that was necessary. Surely "this particular lectern" would have done the job. Schopenhauer's use of "YOU" as opposed to "you" or even "Ludwig V" is similarly fascinating.

Notice that this is not an empirical issue; it is an "a priori" commission - "this genome counts as schopenhauer1". — Banno

Yes. Am I right to suppose that what makes a rigid designator rigid is our decision to keep it rigid, which means following the rule for its use rigidly. It makes a kind of sense, though I can't help wondering what Wittgenstein would have made of it.

I suppose one could think of a genome in that way, but it seems just obvious to me that the link between DNA and the individual who grows from it is empirical; that a fertilized egg is not sentient, not conscious and hence not a person; and consequently that neither schopenhauer1 not anyone else has ever been a fertilized egg (though we have all been a baby). Perhaps there is an argument somewhere in Roman Catholic doctrine about this, but I doubt that I would be inclined to accept it.

I'm curious what you think about natural kinds and causation Ludwig V -- it seems that since continuity of a person is the real underlying topic, though through the lens of the identity of objects (however we wish to construe that), I'm wondering if you believe natural kinds and causation have anything to do with the continuity of a person? — Moliere

I would have thought that causation (broadly understood) would have a great deal to do with the continuity of anything that exists in space and time.

I don't understand what natural kinds are supposed to be. The oft-cited example of water does not help me. In the first place, water is one of three forms of that particular molecular structure - (steam (gas), water (liquid), ice (solid)). Second, there are two forms of water (light and heavy) and no less than eight forms of ice. Third, Putnam's twin worlds seem to demonstrate that it is an empirical fact that water could have more than one molecular analysis, though his hypothesis that we might be unable to tell the difference seems wildly implausible to me. In addition to that a quick look at, for example, the Wikipedia article on this topic indicates that there is a wide range of views about what they are, which means that simply to accept that there are natural kinds is to accept a pig in a poke.

I was under the impression that the continuity of a person is the topic in hand. No doubt the continuity of physical objects is part of that story. But I don't think it is the whole story. See my response to schopenhauer1 below.

Personalities it has been reported, are very much tied to genetics, even though it is also shaped in large part by environment, for example. It is probable that various capacities and abilities are more likely tied to genes than people might admit, etc. — schopenhauer1

When hydrogen and oxygen combine in a process to make water, when water forms, it is now that substance and not its antecedents we are discussing. — schopenhauer1

I take it that you would object to any suggestion that either hydrogen or oxygen is water in any sense. It is only the combination that is water. Equally, each of us is the result of our genes and environment in combination. Your claim that my DNA is me is the same misunderstanding as the suggestion that hydrogen is water. It is the combination of genes and environment that results in the person. To put the point another way, personalities are very much tied to genetics and also to the environment. Both connections have been widely reported and extensively analysed. Bluntly, I am just as much the result of my environment as I am of my genes. After decades of debate about which has priority, there are now some sensible voices that declare that the influence of the two cannot be disentangled.

Even if it was a different sperm that conceived that night a second earlier, that is not you, so the set of possibilities that encompasses the YOU looking back in hindsight is no longer even a fact. — schopenhauer1

I see four issues here.
First, your view that, once the egg is formed, everything is set. I'm not clear whether you intend this is in as a deterministic (causal) thesis or a fatalistic (in Ryle's sense) thesis. Your use of "necessity" suggests the latter, but it isn't really clear which you have in mind. Either way, which fertilized egg results from the process is just as determine/ necessary as what happens after the fertilization takes place. The causal chain does not begin with the event of fertilization any more than it ends when I am fully grown. So I don't see why you want to give any special emphasis to that moment.

Second, in inviting me to look back on my own conception, you have posited my existence as a given. So obviously any egg different from the one that began my process is not me. Just as any clone made from my body is clearly not me. But if I were to posit myself as an outside observer, not involved in the proceedings or, better, as a prospective parent, things look very different. I do not think of the many, many possibilities that there are and which I do not know about. I might care a great deal about various features the baby might or might not have, but I cannot say, when the baby is born, that the wrong one has been born. This harks back to Ryle's point about the difference between the future tense and the present or past tenses.

Third, there is an important difference between people and (inanimate) objects. People participate in their own identity. When they learn the use of "I" and "You" and "S/he/it" (and learning that "I" said by me is the same person as "you" said by you, is a really complicated and critical skill). But this does not depend on any history or social role or personal relationship. It works by responses, not by properties. You could call it the Cartesian self, for the sake of a name. When I learn to respond to my own name and how to use the names of other people, I begin to join society, but that is still not a question of the kind of identity you seem to be interested in; it is a question of my responses to others and the responses of others to me. My identity in this sense is settled by how we respond to each other.

FInallly, the question we started out with is not a question of identity in the usual philosophical sense, but in this Cartesian sense. It is about the "I" that imagines things and what the limits of such an imagination might be. Or at least is related more to that than to my "public" identity. There doesn't seem to be much waiting to be said about it. That explains our diversion to the standard philosophical debate. But the difficulty of imagining myself as a different person clearly plays in to the debate we are actually having.

Oh, this is an actual question about another poster?

No I am not him. Why did you think that? — Apustimelogist

I supposed it is a matter of surprising coincidences. The last time I saw a post from @Srap Tasmaner was a short while before the first post I saw from you and what you were saying seemed like it could well have been a continuation of a line of thinking he had been engaged in.

There is also similarity in posting style.

That, and sock puppet spotting has become a weird hobby of mine, and I've developed a significant degree of trust in my sock puppet spotting intuitions. On the other hand, experience as an engineer has taught me the value of test to failure, and not least in the case of my own intuitions.

Thus my question.

So I think you missed some conversations. I am not really talking about personal identity, though I left it in the title. Rather, I am talking about what it would take for all possibilities of specifically, you (the person reflecting back in hindsight) to obtain, INCLUDING the one in the very present, right now, without it no longer being specifically YOU but someone else. That point is conception of those particular sets of gametes, in that causal-historical space.

We are assuming that there is no such thing in these possible worlds, where exactly the same experiences and genetics are a possibility, though certainly conceivable. Even if that was the case, the fact that that not only clone, but literal, double of every aspect of you down to the millisecond, would still be taking up some causal-historical space that differs, so I think even that is immune, though I don't think it necessary to even worry about that.

I don't understand what natural kinds are supposed to be. The oft-cited example of water does not help me. In the first place, water is one of three forms of that particular molecular structure - (steam (gas), water (liquid), ice (solid)). Second, there are two forms of water (light and heavy) and no less than eight forms of ice. Third, Putnam's twin worlds seem to demonstrate that it is an empirical fact that water could have more than one molecular analysis, though his hypothesis that we might be unable to tell the difference seems wildly implausible to me. In addition to that a quick look at, for example, the Wikipedia article on this topic indicates that there is a wide range of views about what they are, which means that simply to accept that there are natural kinds is to accept a pig in a poke. — Ludwig V

The water example doesn't work for me either. I'm going to try and explain some difficulties here.

From a chemical perspective "water" is an aggregate of H2O's, and it's the aggregate properties which "emerge" when having molar quantities of H2O at temperature-pressure ranges we find on Earth that results in the physical properties that we colloquially refer to as water. And in terms of a theoretical description of a molecule the thing that's missing from the locution "H2O" is the structural relationship between the hydrogens and the oxygen that accounts for its various observed properties. In terms of reference, though, we don't ever really refer to any individual molecule -- we refer to the aggregate of molecules, and so the use of "this" doesn't exactly work very well to my eyes, or at least not as well as it does with the lectern example for me. The individual molecule does not have a name or the identity "water", and so while the molar quantities of H2O form water, if we want to be technical, water is not just H2O but H2O in molar quantities at a certain temperature-pressure point. A single H2O molecule floating across space is not wet, though water is.

I'd say that it's these complexities which don't bear an obvious relationship to the identity of "water". Further I'd say that the case of water is easier than the case of a human being, so figuring out how we're supposed to talk about the identity of water might shed some light on how we might talk about genomes and humans, so I thought I'd go down the route of explaining some of my thoughts in thinking through the difficulty of referencing a technical body of knowledge for the solution of a philosophical problem.

The individual molecule does not have a name or the identity "water", and so while the molar quantities of H2O form water, if we want to be technical, water is not just H2O but H2O in molar quantities at a certain temperature-pressure point. A single H2O molecule floating across space is not wet, though water is. — Moliere

Actually, this gives more understanding of the matter than if it was straightforward 1:1. That is to say, it is necessary for it to be water, but not sufficient. Certainly, without H20, it would not be water, even if various other mechanisms were in place that are involved in molecular bonds, structural relationships that are contingent to the molecular properties, and so on.

Am I right to suppose that what makes a rigid designator rigid is our decision to keep it rigid — Ludwig V

This is to my eye the best way to understand rigidity - as a rule of grammar. It sets out a way of talking about counterfactuals that inherits the coherence of Kripke's formal treatment, while avoidingthe ontological complications of Lewis' account.

My suspicion is that Wittgenstein would agree that whether @schopenhauer1 is essentially his genetics is an issue of how we choose to talk about schopenhauer1, and not an issue of empirical observation, as some seem to think.

Anyways, this is indeed extra-scientific as it is dealing with causality, possibility, and identity. These things are not going to be seen in a microscope or shouted at you from the universe in some way through an equation. Rather, it has metaphysical implications as to how possibilities are carried out over physical things, like objects.

And thus, I take a "natural kind", Moliere, to be something that one can break down into some substance. A chair by itself is a concept that depends on one's notion of what a chair does or how the maker intended it to work. That isn't a natural kind. However, a piece of wood from the chair would be of a natural kind as you can analyze its substance to some physical property. But of course, since ideas, and neurons, and concepts ultimately come from some "physical substrate", it can be argued this too is natural. However, now we are going far afield as it turns into the mind/body problem and how the neurochemical configures are the same as "chair", and we have lost the point of this thread.. Because that argument would not matter to the point I am making.. Once "chair" the concept is found to be a "natural kind" in the neurochemistry, let's say, it too would be subject to this theory as well.

Thus, natural kinds, like humans, and the gametes, are of a substance and a causal instance. At that point where the substance is present, that causal-historical point in time, that becomes the point at which that object can be said to carry with it the possibilities of that object. And thus, you the human looking back to see if you could have lived a counterfactual life, can only go back so far before the very possibility that brought about this person of this substance was no longer even a possibility to begin with. I identified this at the point of conception. — schopenhauer1

Cool. So we at least agree that this is an extra-scientific, or maybe scientific-adjacent, sort of question.

With respect to water there are a number of details that make me question the notion that water actually is H2O, though I can agree to some kind of a posteriori necessity when it comes to individuals.

Actually, this gives more understanding of the matter than if it was straightforward 1:1. That is to say, it is necessary for it to be water, but not sufficient. Certainly, without H20, it would not be water, even if various other mechanisms were in place that are involved in molecular bonds, structural relationships that are contingent to the molecular properties, and so on. — schopenhauer1

I'm not so certain that the account of a posteriori necessity works very well for water, though. Even the water in my cup right now. This is because I tend to agree with Hume on causation -- that it is a habit of ours as creatures who look for patterns, and that tomorrow water could turn out to be something aside from what we thought it was by exploring those patterns. This is a feature of most scientific knowledge: the knowledge is always provisional, and built around technical problems of a particular group of knowledge-producers. If water is H2O, then water is necessarily H2O -- of course! But is it actually H2O?

Do we, by adding all these properties from the various textbooks about water thereby obtain the "essence" of water? Well, not exactly, because now it's just a collection of properties we happen to bundle together into a name, and doesn't have an essential property that makes it what it is. We're interested in it mostly because we're thirsty, and identify it by how it looks and that it is wet, but H2O doesn't look like or feel like anything at all; rather it's a technical classification of what we see and feel.

Well said on these various posts.

Totally agree about this water thing. I more or less have the same idea but I extend it to individuals too.

Ha, have any of your suspicions been verified? I had a suspicion of that kind of nature once about another poster who hasnt posted in this thread, there was just another poster with a very similar writing style who started posting in the same thread as them.

This is to my eye the best way to understand rigidity - as a rule of grammar. — Banno

Well, that resolves one of my difficulties about Kripke. It would be interesting to know whether Kripke thinks that this fits with what he has to say about rules.

Further I'd say that the case of water is easier than the case of a human being, so figuring out how we're supposed to talk about the identity of water might shed some light on how we might talk about genomes and humans, — Moliere

Well, it might be easier - but that doesn't seem to make it easy. One thing that makes it much more difficult is that if you are talking about the person, not just the human being, you are talking about a being that is not passive, but participates in the identity game and has views of his/her own. Many people would think that it is outrageous to reduce (and they mean that word literally) a person to their gametes. Heredity is not identity.

all possibilities of specifically, you (the person reflecting back in hindsight) to obtain, INCLUDING the one in the very present, right now, without it no longer being specifically YOU but someone else. That point is conception of those particular sets of gametes, in that causal-historical space. — schopenhauer1

The gametes issue doesn't take into account the fact that I am a participant in this game; that is, I have views about what possibilities I have and what possibilities would make me a different person and what possibilities would reveal the person that I actually (in my view) am. I'm not saying that I can dictate, but I can certainly demand that my views are taken into account.
Why do you feel the need to write "YOU" instead of "you", and why do you not consider the identity of a third person - not me, not you, but him/her over there? It seems you think it makes a difference.

Ha, have any of your suspicions been verified? — Apustimelogist

Oh yeah. I'd estimate my record at something like 15 and 3. (With one of my failures being dismissing my intuition that I was observing sock puppetry.)

However, a large percentage of my successful recognitions of sock puppetry involved individuals with some degree of personality disorder, which makes for relatively stereotypical behavior patterns. My ratio when there aren't personality disorders involved is definitely lower.

Well, it might be easier - but that doesn't seem to make it easy. One thing that makes it much more difficult is that if you are talking about the person, not just the human being, you are talking about a being that is not passive, but participates in the identity game and has views of his/her own. Many people would think that it is outrageous to reduce (and they mean that word literally) a person to their gametes. Heredity is not identity. — Ludwig V

True. I agree that heredity is not identity.

I think we've both brought up those difficulties with @schopenhauer1, but the response has been more along the lines of when an object is an object. In those terms "water" is easier for me to think through than "human". When or how should a technical body of knowledge be used philosophically?

In terms of using scientific knowledge in a philosophical context I thought "water" might prove easier for us all.

I think it's the notion of "genetics" in a philosophical context that caught me. And that intersection between science and philosophy has always drawn me in.

I'm not so certain that the account of a posteriori necessity works very well for water, though. Even the water in my cup right now. This is because I tend to agree with Hume on causation -- that it is a habit of ours as creatures who look for patterns, and that tomorrow water could turn out to be something aside from what we thought it was by exploring those patterns. This is a feature of most scientific knowledge: the knowledge is always provisional, and built around technical problems of a particular group of knowledge-producers. If water is H2O, then water is necessarily H2O -- of course! But is it actually H2O? — Moliere

The gametes issue doesn't take into account the fact that I am a participant in this game; that is, I have views about what possibilities I have and what possibilities would make me a different person and what possibilities would reveal the person that I actually (in my view) am. I'm not saying that I can dictate, but I can certainly demand that my views are taken into account.
Why do you feel the need to write "YOU" instead of "you", and why do you not consider the identity of a third person - not me, not you, but him/her over there? It seems you think it makes a difference. — Ludwig V

So why I say YOU, is I am discussing the person that has actualized all the events leading to the very present. THIS person (the present you, not a counterfactual you that could have actualized differently), could not have been THIS person without certain factors. As far as the main factor that differentiates the range of possibilities that led to THIS present you from a range of possibilities that would NEVER include the YOU that is present right now, that would be the set of gametes that developed into the current YOU. That is to say, it's as far back as we can go whereby if the circumstances were different (there was a different set of gametes), there was no possible world that the current actualized YOU would have existed as YOU are right now looking back on your life.

And as far as H20 and rigid designators, I think this is more-or-less where the idea stands:

One puzzling consequence of Kripke semantics is that identities involving rigid designators are necessary. If water is H2O, then water is necessarily H2O. Since the terms 'water' and 'H2O' pick out the same object in every possible world, there is no possible world in which 'water' picks out something different from 'H2O'. Therefore, water is necessarily H2O. It is possible, of course, that we are mistaken about the chemical composition of water, but that does not affect the necessity of identities. What is not being claimed is that water is necessarily H2O, but conditionally, if water is H2O (though we may not know this, it does not change the fact if it is true), then water is necessarily H2O. — Rigid Designator

Rigid Designator says "Since the terms 'water' and 'H2O' pick out the same object in every possible world, there is no possible world in which 'water' picks out something different from 'H2O'."

One might agree that "If the terms 'water' and 'H2O' pick out the same object in every possible world, there is no possible world in which 'water' picks out something different from 'H2O'," but wonder how one could prove the antecedent, which is, in old-fashioned terms, empirical, and justify "Since the terms 'water' and 'H2O' pick out the same object in every possible world, ....." Putnam's example of Twin Earth seems to prove that you can't. See also my reply to Moliere below.

THIS person (the present you, not a counterfactual you that could have actualized differently), could not have been THIS person without certain factors. — schopenhauer1

Yes. Kripke does the same thing with his "this very lectern". I don't see the difference, philosophically between THIS person and this person.
We both agree that this person is the result of various factors. But you pick out one of them - admittedly an important one - and sweep away the rest as trivial.

If water is H2O, then water is necessarily H2O -- of course! But is it actually H2O? — Moliere

There's only one way that I can think of that makes sense of this. Essentially, it involves attributing to "possible" the logic that we see in "probable". The latter, at least for the purposes of mathematical theory, is essentially future-looking, because it is defined in terms of a future event - the outcome. The probability of my next throw of the die coming up 6 is 1:6. When I throw the die and it comes up 5, the probability of that throw coming up 6 is 0, i.e there is no probability of that throw coming up 6.
We could say that there is a possibility of club X winning the match against club Y. When club X loses the match, there is no longer any possibility of it winning. (Although you can say, counterfactually, that they might have won.) When the possibility of rain this morning is 60% and it rains, there is no possibility of it not raining. I imagine @Banno will have something to say about this.

When or how should a technical body of knowledge be used philosophically? — Moliere

It is difficult. The answer, in a word, is - cautiously.
One trap is is the adoption of an interpretation of the evidence long before it is certain. So I have seen people, on discovering that there is a deterministic interpretation of quantum theory, announce that we can all now relax, since science has proved that determinism is true.
My other pet hate is people picking up on the latest exciting results announced by a team who are looking for research grants and announcing that science has now discovered ..... It's one thing to look at the wonderful photos of galaxies etc. and quite another to draw conclusions from them. The latter needs good technical knowledge; the former does not.
On the other hand, it seems pretty much common sense that water is H2O and that the COVID virus causes disease. But it is then a mistake to forget that those are discoveries and the world might have been different.
I'm in favour of case-by-case rather than trying to draw up rules.

There's only one way that I can think of that makes sense of this. Essentially, it involves attributing to "possible" the logic that we see in "probable". The latter, at least for the purposes of mathematical theory, is essentially future-looking, because it is defined in terms of a future event - the outcome. The probability of my next throw of the die coming up 6 is 1:6. When I throw the die and it comes up 5, the probability of that throw coming up 6 is 0, i.e there is no probability of that throw coming up 6.
We could say that there is a possibility of club X winning the match against club Y. When club X loses the match, there is no longer any possibility of it winning. (Although you can say, counterfactually, that they might have won.) When the possibility of rain this morning is 60% and it rains, there is no possibility of it not raining. — Ludwig V

Yes on future-looking, but I'm uncertain on probability. If water actually is H2O, for instance, the probability of the statement is 1, and if it is not then it is 0.

My thought is that "water" is the common-sense term and "H2O" is the technical term. Now these do blend in common usage so of course we can use the locution "H2O" as we use the locution "water", but upon thinking about the problem from a technical perspective I'd say that these are two different terms if we want to be strict or philosophical with our usage. "Water", in comparison to Lavoisier, is an ancient word. Though this definition pushes against what I've been laying out:

Water viewed as a chemical substance, regardless of its physical state (and so including ice and steam), now recognized to be a compound of hydrogen (two volumes) and oxygen (one volume) having the formula H2O; (in early use usually) water as one of the four or more elements of ancient and medieval philosophy

But even here I'd note that a chemist differentiates between aqueous solutions and water, and the normal usage calls the sea "water" even though it's actually a mixture of water, ammonia, salt, etc. So that the common usage does not always pick out the very same thing even in our world, and so the claim to necessity is hampered by that possibility.



But I take your point here:

I'm in favour of case-by-case rather than trying to draw up rules. — Ludwig V

that there may not be a comparison between water and people, or H2O and genomes, after all. Fair point.

I believe this addresses common sense? But tell me if not. (EDIT: here thinking that common sense would be covered by the usage of "water", whereas the case against necessity is using "H2O")

Yes on future-looking, but I'm uncertain on probability. If water actually is H2O, for instance, the probability of the statement is 1, and if it is not then it is 0. — Moliere

That's right. And my correspondent on mathematics in general and probability in particular tells me that these are regarded as degenerate cases of probability. I think it is more helpful not to call them any kind of probability, since it is the end of the logical cycle of probability, from uncertainty to resolution.

When you say "if water actually is H2O" you are positioning yourself at the end of a process. I distinguish between possibility and probability as distinct stages in a process. A possibility is what goes into a probability table before it is assigned a probability value; then it is assigned a value and becomes a probability (and not a possibility); then the outcome happens and it becomes either a certainty or a falsehood. The words are not sufficiently strictly defined to defend this as what the concepts actually are; it's just a helpful way to think about them. There are complications, such as the concepts of degrees of confidence and likelihood.

So that the common usage does not always pick out the very same thing even in our world, and so the claim to necessity is hampered by that possibility. — Moliere

I'm afraid common usage is too messy for us. Common usage can distinguish between water, sea water, sewage water, rain water, &c. Pure or distilled water is part of that range, but is really a technical idea, now adopted by common usage. Perhaps we need a natural kind for each of them?

that there may not be a comparison between water and people, or H2O and genomes, after all. Fair point. — Moliere

Well, you're being a bit strict there. I don't think comparisons are really true or false. I prefer to think of them as helpful or not, illuminating or not and so on. I certainly think that, in this conversation, the comparison between water/H2O and people/genomes is unhelpful. Water is H20. But people are not their genomes.

But even here I'd note that a chemist differentiates between aqueous solutions and water, and the normal usage calls the sea "water" even though it's actually a mixture of water, ammonia, salt, etc. So that the common usage does not always pick out the very same thing even in our world, and so the claim to necessity is hampered by that possibility. — Moliere

I'm afraid common usage is too messy for us. Common usage can distinguish between water, sea water, sewage water, rain water, &c. Pure or distilled water is part of that range, but is really a technical idea, now adopted by common usage. Perhaps we need a natural kind for each of them? — Ludwig V

Its interesting because really, we can get arbitrarily specific about different kinds of water. When H2O molecules react it results in various different ions which are essential for its properties so if you want to be more specific, you could say that water isn't really just H2O - that water is H2O may be a straightforward statement since it emerges from H2O molecules interacting, but then it has to be qualified that this is idealizing the details.

https://en.m.wikipedia.org/wiki/Self-ionization_of_water

We might then see that different concentrations of these ions result in different properties of water and then we might have water with different isotopes of hydrogen which impart different properties too.

Seems to me anyone can get as precise as one wants in distinguishing things and all "natural kinds" require ignoring some kinds of details, differentiation, contextual relevance. Nothing we categorize in the world avoids arbitrary abstractions.

I certainly think that, in this conversation, the comparison between water/H2O and people/genomes is unhelpful. Water is H20. But people are not their genomes. — Ludwig V

Got it. So we agree on the latter, at least, and to be honest I'm somewhat hesitant about my distinction between water and H2O, though I think that the claim to necessity is what justifies what would normally be an incredibly inane distinction.

Whereas with people/genome it seems to me that the distinction is fairly obvious: even though the genome plays a critical role in our development that doesn't mean humans are their genome.

I thought about using auto-ionization as an example earlier but then thought that it could be seen as the idealization so I decided to drop it. But if we take auto-ionization as true then, yes, not every molecule in water is H2O -- some of them are H3O+ or OH-, though very little in comparison.

Yes. Kripke does the same thing with his "this very lectern". I don't see the difference, philosophically between THIS person and this person.
We both agree that this person is the result of various factors. But you pick out one of them - admittedly an important one - and sweep away the rest as trivial. — Ludwig V

Because it was that web of circumstances (conception) that is the point of time when the actualized person that is the you right now could have come to be in the first place, EVEN IF you could have had a range of possibilities of counterfactuals after that which led to another "version" of you. Any further back than this, there COULD NOT EVEN have been the actualized version of you now who is looking back. That is my main point.

Seems to me anyone can get as precise as one wants in distinguishing things and all "natural kinds" require ignoring some kinds of details, differentiation, contextual relevance. Nothing we categorize in the world avoids arbitrary abstractions. — Apustimelogist

It just means that H2O represents more than just "H2O" perhaps. That it also represents the other things you maintain. But the point is that it becomes a posteriori necessary, which is Kripke's controversial theory. The evidence provides the necessity of identity's content, which can be changed with more evidence. So the content can change, but the link of necessity does not, with whatever it is that that content provides.