:rofl:

I'm skipping over some of the exploration of Lewis' theory to answer the obvious question: "Is Lewis serious?" The answer is: yes.

2.1.5 A Brief Assessment of Concretism
Lewis's theory is particularly commendable for its striking originality and ingenuity and for the simple and straightforward answers AW1 and AE1 that it provides to our two questions QW and QE above. Furthermore, because worlds are (plausibly) defined entirely in nonmodal terms, the truth conditions provided by Lewis's translation scheme themselves appear to be free of any implicit modality. Hence, unlike many other popular accounts of possible worlds (notably, the abstractionist accounts discussed in the following section), Lewis's promises to provide a genuine analysis of the modal operators.

Perhaps the biggest — if not the most philosophically sophisticated — challenge to Lewis's theory is “the incredulous stare”, i.e., less colorfully put, the fact that its ontology is wildly at variance with common sense. Lewis faces this objection head on: His theory of worlds, he acknowledges, “does disagree, to an extreme extent, with firm common sense opinion about what there is” (1986, 133). However, Lewis argues that no other theory explains so much so economically. With worlds in one's philosophical toolkit, one is able to provide elegant explanations of a wide variety of metaphysical, semantical, and intentional phenomena. As high as the intuitive cost is, Lewis (135) concludes, the existence of worlds “ought to be accepted as true. The theoretical benefits are worth it.”

Additional discussion of, and objections to, concretism can be found in the supplemental document — ibid

As a science fiction fan, the idea of modal realism doesn't seem all that strange. Protagonists are forever waking up in the wrong world, with much drama resulting. But on what basis do I accept the idea? According to Lewis, in spite of it's being ontological inflation, it's the simplest explanation for the way we think about modality. I think I agree with this.

Haecceity in itself could not account for transworld identity, because haecceity describes an individual being what it is, in all its uniqueness. Haecceity is the identity of the individual in all of its uniqueness. Therefore each individual would have a unique haecceity, and unique identity in each possible world.

If we say that a thing's haecceity is its essential properties, and this provides for transworld identity, as your referred article seems to imply, then we don't have a thing anymore, no de re, just Platonism, ideas, things said. — Metaphysician Undercover

No. As described in the article I had linked to (here again), haecceity is just a bare identity, not decomposible into a set of one or more things or properties. It is essence, but not comparable to other theories of essence, except for contrasting it.

Under this theory, your haecceity could have been actualized in King Charles, a dog, an amoeba or a quark.

As an ontological theory, I think it's ridiculous. It seems to be arrived at by process of elimination: take away each of your non-essential parts and properties, and what's left? I say, nothing. But someone committed to transworld identity say that haecceity is what's left.

The SEP article was written by Penelope Mackie. I read her book "How Things Might Have Been". She does a good analysis of the problems with essences, and distills it down to this being the inly viable form- iff one is willing to accept it. I don't know if she really believes it, or if it's just a foil.

No. As described in the article I had linked to (here again), haecceity is just a bare identity, not decomposible into a set of one or more things or properties. It is essence, but not comparable to other theories of essence, except for contrasting it. — Relativist

But haecceity then cannot account for transworld identity. Transworld identity must allow that the same thing has different properties at the same time, is different in different worlds. The transworld thing would require multiple haecceities, because haecceity includes all the unique properties of the thing. I actually couldn't understand how the proposal works. They speak about haecceity as if it is traditional "haecceity", the unique identity of an individual, but then they also say it's like an essence, which appears Platonic. If you could explain it to me in a way which makes sense, I'd appreciate it.

As an ontological theory, I think it's ridiculous. It seems to be arrived at by process of elimination: take away each of your non-essential parts and properties, and what's left? I say, nothing. But someone committed to transworld identity say that haecceity is what's left. — Relativist

The concept of haecceity is the opposite of this though. It includes each and every property which makes an individual the unique thing it is, including both essential and accidental properties, as well as external, spatial temporal positioning.

If you take away all properties, then what's left is matter, potential. But it would be the same matter for everyone and everything, and nothing would distinguish one from another.

But haecceity then cannot account for transworld identity. Transworld identity must allow that the same thing has different properties at the same time, is different in different worlds — Metaphysician Undercover

Read literally, what you've written makes no sense. I think what you trying to say that IF there is transworld identity, then an object can have the same identity in 2 different worlds, despite having a different set of properties in each world. I agree that is what transworld identity means.

Haeccety (if it exists) is a non-qualitative, non-analyzable property. It is the one and only necessary and sufficient property that an identity has. So if haeccetism is true, then all the qualitative properties are superfluous to the identity. In comparing two possible worlds, the object could be qualitatively entirely different between the worlds - but it would be the same object (same identity) as long as the particular haeccety is present.

I am correcting what I said before: I had conflated haeccity with bare identity. They are very similar, but subtly different.

As an ontological theory, I think it's ridiculous. It seems to be arrived at by process of elimination: take away each of your non-essential parts and properties, and what's left? I say, nothing. But someone committed to transworld identity say that haecceity is what's left.
— Relativist

The concept of haecceity is the opposite of this though — Metaphysician Undercover

I refer you to the article's definition of haeccitty:

The view that an individual’s transworld identity is ‘bare’ is sometimes described as the view that its identity consists in its possession of a ‘haecceity’ or ‘thisness’: an unanalysable non-qualitative property that is necessary and sufficient for its being the individual that it is.

"Thisness", usually.

Seems to me the epitome of philosophical reification.

As a science fiction fan, the idea of modal realism doesn't seem all that strange. — frank

His theory of worlds, he acknowledges, “does disagree, to an extreme extent, with firm common sense opinion about what there is” (1986, 133). However, Lewis argues that no other theory explains so much so economically. SEP Possible Worlds

Just a thought, but Lewis’s approach seems very similar to that of Direct Realism.

Lewis argues that because the concept of concrete possible worlds explains so much and so economically, this overcomes any common sense objections we may have to it.

Similarly for the Direct Realist, who argues that the tables and chairs we perceive are ontologically real, rather than indirect representations, because this explains so much and so economically.

True, although isn't there an extra conundrum with direct realism: that if it's true, then it must be false (by virtue of what we observe about how the senses work).

So, what's Haecceity?

It's what a thing has that makes it what it is.

So, what is it that a thing has that makes it what it is?

Well, Haecceity, obviously.

And... what's Haecceity...?

And so on. — Banno

Very good. But of course, rejecting one proposal does not resolve the problem of transworld identity. Nor does it make any other proposal more reasonable. The obvious fact is that "possible worlds" is a faulty interpretation of "possibility" based in a Platonism which violates the law of identity. Therefore the problem will never be resolved, even if "possible worlds" remains very useful for sophistry.

Haeccety (if it exists) is a non-qualitative, non-analyzable property. It is the one and only necessary and sufficient property that an identity has. So if haeccetism is true, then all the qualitative properties are superfluous to the identity. In comparing two possible worlds, the object could be qualitatively entirely different between the worlds - but it would be the same object (same identity) as long as the particular haeccety is present. — Relativist

OK, I think I see what you are saying. I understood "haecceity" as what makes a unique thing the unique thing which it is. And that is somewhat correct, but I understood this to be a compilation of all the thing's distinct properties. You are proposing that it is something distinct form all of the qualitative properties, a special sort of property which gives a thing its uniqueness. Isn't this sort of contradictory? How could there be a non-qualitative property? It's like the thing has a property which is not a property. Or is it a property which we could never know because we know things by their qualitative properties?

Nevertheless, I think the problem I mentioned remains. This is similar to if we say that a thing's matter is what provides for its identity, uniqueness, or haecceity. Matter is distinctly not a qualitative property, it is some sort of underlying substance. We say that each thing is composed of matter, and we say that it's a fact that this matter in this thing is unique, and not the same as that matter in that thing, which ultimately gives a thing its uniqueness, individual identity, or haecceity.

Now, the problem is that "matter" itself is just a concept. it is the most universal concept because we say that every thing has matter, so it does not provide any principle for us to distinguish one thing form another. At the level of matter, everything is the same, because we use properties to distinguish one thing from another, and at that level, everything is just "matter". So "matter" and "haecceity" are both useless as principles of identity. The proposition that "matter" itself, without any form, or that "heaccceity", is what accounts for a thing's identity, is like saying that a thing is unidentifiable.

So if haeccetism is true, then all the qualitative properties are superfluous to the identity. In comparing two possible worlds, the object could be qualitatively entirely different between the worlds - but it would be the same object (same identity) as long as the particular haeccety is present. — Relativist

This is a good example of the problem I mentioned above. It's basically the problem of infinite possibility. You say "the object could be qualitatively entirely different between the worlds". Well, so could every object. So there is nothing then to distinguish one object from another, between worlds. We claim there is something, "haecceity", but we can't know it. Then we are left with arbitrarily, or subjectively assigning names to bundles of properties.

We start with the opposite of bundle theory, and end up being the very same as bundle theory. We start with the assertion that there is an underlying substance, matter or haecceity, which makes a thing the thing it is. Then we realize it is impossible for us to know this underlying substance, from the way it is defined, as other than a property, so it gets left as useless to our knowledge. Therefore within our epistemology, the thing becomes a bundle of properties without any underlying substance. Haecceity, as defined, cannot serve its purpose.

Lewis argues that because the concept of concrete possible worlds explains so much and so economically, this overcomes any common sense objections we may have to it. — RussellA

Lewis' way, of concrete possible worlds, appears to be the only way to escape Platonism and idealism in general, once the "possible worlds" model is accepted. But it's not a real escape. The problem being that the possible worlds model produces a separation between the possible worlds and the actual ontological world. Then one has to be selected as the real. Once the possible worlds are selected as the real, we get multiverses, etc.. The only true escape is to reject "possible worlds" as a faulty interpretation of possibility.

"Thisness", usually.

Seems to me the epitome of philosophical reification. — Banno

You've taught me another new word, and I thank you for that - "reification" -

"treating an abstract idea as if it were a concrete, real thing."

My first question is this - just because something is not concrete, does it follow that it cannot be real?

I'm looking at this through the lens of my biology background - in which all living things, and all parts of living things, are described in terms of structure and function, and structure complements function.

So, if we consider the structure of the human brain, its function is to produce a "mind." And the "haecceity" - or the "thisness" of each individual person results from the mental output of the mind. The "mind" is not a concrete thing, but it's real. Indeed, it produces the only reality we know.

Since we each one of us have our individual take on reality, the mind is the set of our "thisness" - or our haecceity.

Or have I misunderstood in limiting "haecceity" to the concept of consciousness?

The problem being that the possible worlds model produces a separation between the possible worlds and the actual ontological world. Then one has to be selected as the real. — Metaphysician Undercover

As I understand it, for Lewis, it is not necessary to select one of the possible worlds as real, as all possible worlds are as real as each other. All possible worlds are real concrete worlds, actual ontological worlds.

SEP - Possible Worlds
But, for the concretist, other possible worlds are no different in kind from the actual world

As an analogy, the world you live in is more than likely very different to the world I live in (the people you know, the history of your country, the local climate, the geography, the architecture), but it would be wrong to say that your world is more real than my world.

This is a good example of the problem I mentioned above. It's basically the problem of infinite possibility. You say "the object could be qualitatively entirely different between the worlds". Well, so could every object. So there is nothing then to distinguish one object from another, between worlds. We claim there is something, "haecceity", but we can't know it. — Metaphysician Undercover

The people engaging in the possible world analysis know which object they are referring to: it's a footballer in one world, a cockroach in the other. So "infinite possibility" is the point: possible world analysis of an object has no bounds. Of course, this means there are no ontological cross-world identities. (This doesn't prevent us from entertaining fictional possible worlds).

Consideration of haeccitism establishes an extreme: no qualitative properties are necessary for holding a particular identity (albeit it requires the questionable assumption that identity is associated with a non-qualitative property).

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.

Is there a viable alternative between the extremes? I don't think so.

True, although isn't there an extra conundrum with direct realism: that if it's true, then it must be false (by virtue of what we observe about how the senses work). — frank

Even though quarks cannot be directly observed through the senses, they are accepted as being real because they explain so much and so economically.

Lewis is also saying that his theory, even if not empirically verifiable, because it is so elegant and explanatory should not be dismissed because it initially seems to be against common sense.

Furthermore, because worlds are (plausibly) defined entirely in nonmodal terms, the truth conditions provided by Lewis's translation scheme themselves appear to be free of any implicit modality. Hence, unlike many other popular accounts of possible worlds (notably, the abstractionist accounts discussed in the following section), Lewis's promises to provide a genuine analysis of the modal operators. — ibid

That bit has me intrigued. A world is a unit such that none of its parts are not "spatiotemporally related to anything that is not also one of its parts". No modality is involved in that definition... at least explicitly. Something is necessary if it is true in all possible worlds. That quantification, for Lewis, is just over ordinary objects inhabiting other worlds. Modality is for Lewis just quantification. It means “true everywhere” rather than “could not have been otherwise”. So Modality is reduced to quantification.

In other systems, modality remains primitive, unreduced.

~~

Very good. But of course, rejecting one proposal does not resolve the problem of transworld identity. — Metaphysician Undercover

"The problem of transworld identity" is a result of your misunderstanding. Try to follow this.

Kripke and I would say that "What if Nixon didn't win the 1972 election?" is a question about Nixon. Those who accept haecceity might say that it was not a question about Nixon, but about Nixon's haecceity, which makes Nixon, Nixon, and not some other thing. Do we have one thing or two here?

So

just because something is not concrete, does it follow that it cannot be real? — Questioner

Do we have one thing, Nixon, or two things, Nixon and that-which-makes-Nixon-what-he-is-and-not-another-thing?

I'll opt for one thing, not two.

And that's the issue with reification - it multiplies entities beyond necessity.

Now to be sure, Occam's principle is more an aesthetic than a logical principle, but I think it applies here. I can't see what explanatory value there is in invoking haecceity. Rather, it shifts whatever issue there might be along one step, giving the mere illusion of an answer.

But someone committed to transworld identity say that haecceity is what's left. — Relativist

I don't see that haecceity is needed at all to explain transworld identity. Indeed, i have trouble seeing that there is an issue here. 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.

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.

...but entertaining it does not entail that it was truly possible. — Relativist

I wonder if you follow this thread from the start.

The word "truly" should fill a philosopher with dread. The whole of the logic set out here is exactly about what is in truth possible. What we are doing here is using Tarski's approach to truth in order to set out a coherent consistent way of talking about modality. "Truth" is built in to the very structure by it's reliance on Tarski's system.

Temporal logic takes possible world semantics and applies it in a temporal context. It uses the very same basis that we have here. The usual order of operation is to work out what we're doing in the modal logic and then to treat temporal logic as a subclass. There is SEP articles on this topic that will explain this, but essentially what they do is set up rules of access between past present and future.

....what is it that makes any object the SAME object — Relativist

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.

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

Transworld identity or counterpart theory is not discovered by the model, it is presupposed by the interpretation function. This is a central feature of the logic we have been studying, and accepted by both Kripke and Lewis. Both Kripke and Lewis agree on this point; they diverge only in how identity should be metaphysically understood. The difference is in whether that identity is set by rigid designation or by counterpart theory.

Just to be clear, there is a difference between Kripke's semantics on the one hand, and which is accepted by both Kripke and Lewis, and pretty much everyone else except Meta; and the further, metaphysical approach taken differently in Naming and Necessity and in Lewis' work. The logic is shared. The metaphysics differs.

Filling out that last point, Kripke and Lewis give different ontological readings of the same formal machinery. Their logic is the same, but the metaphysical story differs.

Kripke (Naming and Necessity):

• Proper names refer rigidly to the same individual across worlds.
• Necessity is primitive and tied to rigid designation.
• Modality is not reduced to something non-modal; it is taken as metaphysically basic.

Lewis (Modal Realism / counterpart theory):

• Worlds are concrete; individuals do not literally exist in more than one world.
• Identity across worlds is determined via counterpart relations.
• Modality is reduced to quantification over concrete worlds.

Shared Logic / Semantics

• Possible worlds semantics: Both use worlds as the basis for evaluating modal statements.
• Quantified modal logic: Both accept first-order quantification over individuals.
• Transworld reference: Both presuppose a way to interpret identity or counterparts across worlds.
• Truth-at-a-world: Both define modal truth in terms of what holds at particular worlds.
• Accessibility relations: Both can accommodate structured relations between worlds (for temporal or metaphysical distinctions).
• Formal rigour: Both agree that modal claims can be modelled systematically, independent of metaphysical interpretation.

Summarised by ChatGPT

Do we have one thing, Nixon, or two things, Nixon and that-which-makes-Nixon-what-he-is-and-not-another-thing?

I'll opt for one thing, not two. — Banno

I would say that the function (the mind) cannot be separated from the structure (the brain) so we have one thing, not two things. It's not a dualism.

I would also say that of the billions of brains that have ever existed, no two were structurally identical, so the mental output is unique to each individual.

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.

Kripke (Naming and Necessity):
Proper names refer rigidly to the same individual across worlds.
Necessity is primitive and tied to rigid designation.
Modality is not reduced to something non-modal; it is taken as metaphysically basic.


Lewis (Modal Realism / counterpart theory):
Worlds are concrete; individuals do not literally exist in more than one world.
Identity across worlds is determined via counterpart relations.
Modality is reduced to quantification over concrete worlds.

Shared Logic / Semantics
Possible worlds semantics: Both use worlds as the basis for evaluating modal statements.
Quantified modal logic: Both accept first-order quantification over individuals.
Transworld reference: Both presuppose a way to interpret identity or counterparts across worlds.
Truth-at-a-world: Both define modal truth in terms of what holds at particular worlds.
Accessibility relations: Both can accommodate structured relations between worlds (for temporal or metaphysical distinctions).
Formal rigour: Both agree that modal claims can be modelled systematically, independent of metaphysical interpretation. — Banno

Which do you think is closer to approximating the way we really think about modality?

— Relativist

A rigid designator refers to a specific individual in this world[/quote] A rigid designator refers to the very same individual in every world in which it exists. This, pretty much regardless of the properties of that individual. That's the point. Here's the logic common to rigid designators and counterparts. We have in possible world semantics the definition that ☐f(a) if true will be true in all possible worlds. That's the logic. ☐f(a) is true at a world w iff f(a) is true at all worlds accessible from w. Now what, exactly, does "a" represent? The interpretation must supply a rule that tells us how the denotation of “a” at w₀ figures in the evaluation of f(a) at w₁. So we have two interpretations. For Kripke, "a" is a name that refers to the very same individual in every world in which it exists. It rigidly designates that individual, regardless of whatever predicates it might have - regardless of if it satisfies "f" or not. For Lewis, in any possible world w₁ there may be an individual which is maximally similar to "a" is w. That's the individual to which "a" refers in w₁.[code]
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.

This, pretty much regardless of the properties of that individual. That's the point.

Here's the logic common to rigid designators and counterparts. We have in possible world semantics the definition that ☐f(a) if true will be true in all possible worlds. That's the logic. ☐f(a) is true at a world w iff f(a) is true at all worlds accessible from w.

Now what, exactly, does "a" represent? The interpretation must supply a rule that tells us how the denotation of “a” at w₀ figures in the evaluation of f(a) at w₁.

So we have two interpretations. For Kripke, "a" is a name that refers to the very same individual in every world in which it exists. It rigidly designates that individual, regardless of whatever predicates it might have - regardless of if it satisfies "f" or not.

For Lewis, in any possible world w₁ there may be an individual which is maximally similar to "a" is w. That's the individual to which "a" refers in w₁.

Which do you think is closer to approximating the way we really think about modality? — frank

The second is closer to my way of thinking, for the reasons I gave - "Banno might not have answered your post" is a sentence about me, not a sentence about some other bloke in some other world who just happens to be similar to me in certain ways.

I find that argument pretty convincing. So Kripke, not Lewis.

Others find it less convincing.

Others find it less convincing. — Banno

I'm not sure how popular Lewis' view is. It's kind of nutty.

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.

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

Then I'm afraid you have misunderstood something.

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.

I'm not sure how popular Lewis' view is. It's kind of nutty. — frank

Yeah, but technically very clever. It explains the modal operators, rather than taking them as fundamental. They are just a broader quantification across the worlds. It's very neat. But yes, quite mad.

You simply assume it's the same. — Relativist

Not me, Kripke. Again, that it is the same individual in some way is inherent in the definition of possibility and necessity: fa is necessarily true if a is f in every possible world in which it occurs.

If a is going to be f in every possible world, then we have to be able to talk about a in every possible world. How do we do that?

Simple answer: "a" refers to a in every possible world that includes a. More devious answer: "a" refers to a different but corresponding individual in each world.