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. — Relativist

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.

One of the things happening in this side conversation is that modality, temporality and causality are being mixed together with little clear idea of how they interact - that is, without a suitable logic.

One of the great advantages of possible world semantics is that it can be used to provide such logics.

The composition may change in terms of NaCl, etc., but if you do not have H2O then you do not have water. Your response? — NotAristotle

Please take a look at my earlier response to this. But I like to address this in a little different way.

Let us say some fictitious community commonly calls a particular liquid "warder". One day they decide to place the liquid in a pot and place it over a fire to see what would happen. After several hours, they notice the liquid was gone, and there was a white powder remaining. In amazement, they thought the liquid was transformed in the white powder by the heat of the fire. They called this powder "warder" as well, for them it was just a transformation into a different physical state, a solid.

Centuries past, the community developed an Atomic Theory of Matter. Soon they discovered that the liquid they called "warder" was composed of 98% H2O and 2% NaCl. When they perform the same experiment of heating in the pot, they discovered the white powder they called "warder" was compose of 100% NaCl. But even with this discovery, they continue to refer to both liquid and white power as "warder". Have they made some error in this case? What is the nature of this error? Scientifically there is no error, the composition they got right. An error in naming? But one can use the same name to refer to multiple object anytime in language, context will clarify any confusion. If you say there was some metaphysical error committed here, well what was it? I don't think we can make any sense of what a "metaphysical error" would be in this case.

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.

it ignores the controversies... — Relativist

Clarifies, would be a better word.

Your

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. — Relativist

is pretty much right. Contingency is modal, potential is causal, such that if we mix the two, then we ought keep close track of which is which.

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

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.

RIghto. Carry on.

Sure, but in the situation we're talking about every possible world is actual, and there's no definition as to what actual means. So "actual" is meaningless. — Metaphysician Undercover

That is like saying because there is no definitive definition of “pain” the concept of pain becomes meaningless.

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Then there is the source of my empirical experience, which is not one of the possible worlds (as these are what are in the model), therefore not actual. So I concluded that it is an illusion. — Metaphysician Undercover

No one has directly seen a quark, but only theorised about them. The Merriam Webster dictionary defines “illusion” as “something that deceives or misleads intellectually”. “Illusion” would be the wrong word to describe our understanding of quarks. Similarly with theorised possible worlds.

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

No, the actual world we live in is not actual, the possible worlds are actual. — Metaphysician Undercover

It depends what the expression “the actual world we live in” is referring to.

Is it referring to i) the world as we perceive it through our senses or ii) the external world that is causing our sensations?

The reasoning is inescapably circular! — Relativist

There is an escape.

Essence does not play a part in Kripke’s Rigid Designator.

As the Wikipedia article of Naming and Necessity writes:

Kripke's theory of naming, presented in his book "Naming and Necessity," argues against the descriptivist theory of names, proposing instead that names refer to objects through a causal chain originating from an initial act of naming. This means that a name's reference is fixed by its original use, rather than by a set of descriptive properties associated with the name.

Hesperus is Phosphorus is necessarily true as both refer to the same thing, Venus. That Hesperus and Phosphorus have the same identity is only known a posteriori because of empirical observation.

In Kripke’s theory of naming, there is an initial naming of a person, their baptism. In a sense, JL Austin’s performative utterance.

There is then a recursive process, a causal link between this baptised object and future objects.

For example, in possible world 5, there is a causal chain going back from Aristotle 5 to the original baptised Aristotle, meaning that Aristotle 5 is necessarily baptised Aristotle. In possible world 9, there is a causal chain going back from Aristotle 9 to the original baptised Aristotle, meaning that Aristotle 9 is necessarily baptised Aristotle. Therefore, Aristotle 5 is necessarily Aristotle 9. This means that Aristotle is a rigid designator because necessarily and causally linked to all other Aristotles.

Thereby, the baptised Aristotle = casually linked to {Aristote 1 in possible 1, Aristotle 2 in possible world 2, Aristotle 3 in possible world 3, etc}

This is an extensional definition. No intensional definition is required.

Knowing that baptised Aristotle is causally linked to Aristotle 1 tells us nothing about Aristotle’s essence.

For example that a snooker ball moves when hit by a snooker cue tells us nothing about the intrinsic nature or essence of either the snooker ball or snooker cue.

Kripke's Rigid Designator avoids such philosophical problems as to the nature of essence because based on a particular theory of naming.

You're conflating possibility with potential. — Relativist

As I explained, it's ontological possibility, and this is very similar to "potential", but potential I consider to be the broader term than ontological possibility.

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. — Relativist

Sure, all physical things and actions can be understood as "contingent". That means their existence is dependent on causation. The point though, is that by the nature of time, once a contingent action occurs, it is impossible that it did not occur. Therefore the nature of time is such that, as time passes something which is seen to be contingent (existing only as an idea, and requiring causation), may become necessary (having physical existence).

Because of this (the nature of time), it is incorrect to talk about past activities, which are known to be true, as possibilities. Such things do not fulfill the criteria of ontological possibility (they are impossible to be otherwise), nor epistemic possibility (they are known to be true).

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

Yes, E "was" contingent, and both E and ~E "were" possible. Notice the use of the past tense. However, we cannot represent both "E and ~E as possible" now, accept by epistemic possibility. If we do not know which is the case. We know that it is possible that either E or ~E occurred, and by the law of excluded middle it is necessary that one or the other is the case, but we do not know which. That is the basis of epistemic possibility. then we can use logic to try to figure out which. At that time though, when it was present, then both E and ~E were possible in the ontological sense. In this case, when it is at the present and neither one has occurred, neither one is necessary, and the law of excluded middle is violated.

So there is a significant difference between epistemic possibility and ontological possibility. One violates the law of excluded middle the other does not. And, in the case of "E and ~E were possible", at that time referred to in the past, if we know which one occurred, then there is no epistemic possibility. When we look back in time, and we know what happened, even though the event "was" contingent, it is now known as necessary, there is no "possibility" involved in any sense of the word, and alternatives are counterfactuals.

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

How could that possibly be an advantage? You just plunge yourself deeper into the fantasy world of Platonism, and completely disrespect the reality of temporality. Advantage for what, sophistry?

One of the things happening in this side conversation is that modality, temporality and causality are being mixed together with little clear idea of how they interact - that is, without a suitable logic. — Banno

Exactly, it is "without a suitable logic". This is because the logicians prefer to drift off into their fantasy world of Platonism, with complete disrespect for what the metaphysicians are telling them. Some will even say that metaphysics is an unnecessary waste. And so, we are left without a suitable logic to deal with temporal reality.

One of the great advantages of possible world semantics is that it can be used to provide such logics. — Banno

Obviously that is false, "possible worlds" cannot provide that. It completely distances itself from temporal reality by not distinguishing between the sense of "possibility" which violates the law of excluded middle (ontological possibility), and the sense of "possibility" which does not violate the law of excluded middle (epistemic possibility). Further, it allows within that muddled mix in the concept of "possibility", a contradictory sense of "possibility", the counterfactual, which is not a "possibility" in any real sense.

Clearly "possible worlds" in itself, cannot provide for these three very different senses of "possibility". It might provide for one of those senses, but then the others require something different, due to the substantial difference between them. It is the matter of trying to squeeze all these substantially different senses of "possibility" into one "possible worlds" model, which causes the problem.

That is like saying because there is no definitive definition of “pain” the concept of pain becomes meaningless. — RussellA

You left out the other condition, "pain" must refer to everything as well. If pain refers to everything, as "actual" refers to all possible worlds, and there is no definition for "pain", then it's meaningless.

No one has directly seen a quark, but only theorised about them. The Merriam Webster dictionary defines “illusion” as “something that deceives or misleads intellectually”. “Illusion” would be the wrong word to describe our understanding of quarks. Similarly with theorised possible worlds. — RussellA

I disagree, I think quarks are illusory. They exist as theoretical particles, but cannot be produced for observation due to the strong force. What is indicated is that the strong force is not understood, and mass in general is not understood, and "quarks" are just posited to account for that lack of understanding. The concept of "quark" misleads intellectually, by producing the illusion that something not understood is understood.

Is it referring to i) the world as we perceive it through our senses or ii) the external world that is causing our sensations? — RussellA

It doesn't matter. Even the experience of our perceptions must be put into descriptive words before it becomes a part of the modal model. If the modal model is "the actual", then our perceptions are not.

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.

You left out the other condition, "pain" must refer to everything as well. If pain refers to everything, as "actual" refers to all possible worlds, and there is no definition for "pain", then it's meaningless. — Metaphysician Undercover

There is a difference between “pain refers to everything” and “pain refers to everything that is painful.”
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The concept of "quark" misleads intellectually, by producing the illusion that something not understood is understood. — Metaphysician Undercover

Perhaps that is true. In the same vein, every concept we have misleads intellectually by producing the illusion that something not understand is understood.

For example, we have the concept of numbers, but who knows what a number is. We have the concept of pain, but who knows what pain is. We have the concept of consciousness, but who knows what consciousness is.

All concepts may mislead us, but what other choice do we have?
===========================================================================

Even the experience of our perceptions must be put into descriptive words before it becomes a part of the modal model. If the modal model is "the actual", then our perceptions are not. — Metaphysician Undercover

I perceive that the sun is shining. In my actual world the sun is shining.

I imagine a possible world in which the sun is not shining. It is possible that there is an actual world where the sun is not shining.

Actual worlds may exist or possibly exist.

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.

In standard modal logic there is exactly one actual world. Meta's supposing otherwise is another misunderstanding. We've a set of possible worlds, W, and we can label any one of these the actual world, w₀.

In terms of modality, w₀ is not treated any differently to any other world within the formal semantics. It's a convention of the interpretation, an indexical, like "here" or "now"; a thing of convenience. It usually marks the place who's access relations we are considering

What we haven't looked at much is how accessibility works. It's not mentioned much in the article. Accessibility is the relation that sets out which worlds we can "get to" from a given possible world.

So if I am about to flip a coin, I am in a world that can access a world in which the coin comes up "heads", or a world in which the coin can come up "tails". Both are available. But if I just flipped a coin, and it came up "tails", the possible world in which it came up "heads" is no longer accessible.

Importantly, accessibility is not causal, temporal, or epistemic unless specified. And it can be so specified. It constrains what worlds we have access to.

Let's look at temporal logic. A simple temporal logic sets the accessibility relation between possible worlds so that one possible world is the past and other possible worlds are the future. From the past world, many future possible worlds are accessible. But from those future worlds, only one past world is accessible.

We might specify w₀ as now, and various other worlds as possible futures and pasts. In our world it is true that Caesar crossed the Rubicon, and if we want to model history, we stipulate that we cannot access those worlds in which he disbanded the 8th and returned to Rome. But if we want to write an historical fiction, we would thereby access a world in which he did just that. The access relations depend on what it is we wish to model.

To be clear, there are a range of temporal logics, and which you make use of depends on what it is you wish to model. This is just one example.

And there are similarly logics that model causation in terms of accessibility. Lewis constructed such a logic. The coin flip mentioned earlier is a simple example of one possible approach, but there are many others.

The take-away: the structure of possible world semantics that Kripke set up has been used to formalise a wide variety of situations by amongst other things constructing suitable accessibility relations. Since these are dependent on the core possible world semantics, it might be good practice to make sure we understand what that is before we go off talking about these applications of that logic.

Folk hereabouts who jump to causation and temporality quickly become quite muddled.

Hi Richard,

I am not sure if I am well-versed enough in Kripkean semantics to respond to your objection. That being said, here are my thoughts:

Your objection appears to be that all instances of water are some mixture. And, if all instances of water are some mixture, and if it is impossible to refer to a part of a mixture, then it is impossible to refer to a part of "water mixture," namely, the part that is H2O. Compositionally and scientifically, you claim, water is not H2O. But if water is not H2O, then we appear to be limited to identity claims that we could know a priori (i.e. H2O is H2O) and cannot have access to a posteriori necessary truths. It is an interesting objection.

I think intensionality is relevant in matters of reference. My point here is that, when I refer to water, what I am referring to, what I mean, is not the NaCl or the mud or whatever else is in the water, what I am referring to is the H2O stuff. In that case, maybe I can refer to a part of a mixture. I think if you take the view that reference is fixed by the thing that is referenced, then the issue becomes an issue. In other words, if my composition of H2O and NaCl is what determines what I am referring to, then yeah, that would also determine what is meant by water. On the other hand, if what I mean by water is in some sense prior to or co-relational to the thing in the world that is being picked out, then I am not so sure that we have to use the actual-world instantiation of something when we refer.

The SEP article on rigid designation discusses another objection. The objection there is that water is H2O is in terms of content the same semantic statement as H2O is H2O. But if this were the case, that water is H2O would again appear to fail to be an a posteriori claim about the world. However, I think that this objection, similarly to yours, defines reference as an extensional matter; that is, as being based on what is in the world out there. If instead intensionality factors into reference, it seems that we can refer to the stuff that is water without meaning the stuff that is H2O even though water is H2O.

Would be interested to hear what you think about it.

Have they made some error in this case? — Richard B

My sense is that: yes, an error was made. The community thought that the stuff that was NaCl was H2O in a solid form, they were incorrect. They can refer to both as warder as long as they don't mean "H2O is NaCl" if they were to say "warder is warder."

Looks right.

My point with the example is prior to any Atomic Theory of Matter, the community can name the liquid and solid to assist in identifying macroscopic objects and processes without any consideration of microscopic structures. In the example, they simple refer to what is a clear liquid and a white powder and name both “warder”. The name functions for them, “Go fetch me a bottle of ‘warder’ from the shelf so I can perform the experiment” or “After the transformation, warder became a solid powder.” Naming in this example serves the community to identify macroscopic objects to fetch, focus attention, or call out. Knowledge of the composition of both need not stop one from using such a name to carry out these functions. There is no need to appeal to essences in all possible worlds to understand what the name is referring to in this example.

This is why I say there is no error in naming.

The composition may change in terms of NaCl, etc., but if you do not have H2O then you do not have water. Your response? — NotAristotle

Another way to answer this is "if you do not have H2O you do not have H2O, but something can always be named "water".

But please provide your response to this: If you discovered "air" is composed of 78% Nitrogen, 21% Oxygen and 1% Argon, what is rigidly designated in every possible world? Which one do you say, if you don't have X you do not have "Air"?

It seems you cannot use the same rationale like you do for "water", the most dominant component.

I think the real answer here is it does not matter what you say, only what we humans agree upon. Wittgenstein in PI 49 says something similar, "But I do not know whether to say that the figure described by our sentence consists of four or of nine elements! Well, does the sentence consist of four letters or of nine? And which are its elements, the types of letter, or the letters? Does it matter which we say, so long as we avoid misunderstandings in any particular case?"

Would be interested to hear what you think about it. — NotAristotle

There is a good quote from the Introduction in Noam Chomsky's book "Cartesian Linguistics" by James McGilvray that I find useful in this case:

“This is because, as Chomsky suggests, in the domains of mathematics and the natural sciences, one finds strong ‘normative’ constraints on same-use, constraints not found in the use of natural language, where people employ and enjoy linguistic creativity. Everyday speakers are not engaged on a unified project. And as Chomsky also points out, it is no surprise that Fregean semantic theories – those that suppose a community with shared thoughts and shared uniform symbols for expressing these thoughts, and an assumed constraint to be talking about the same thing whenever they use a specific symbol – work quite well with mathematics and the natural sciences. But they do not work with natural languages, a hard lesson for the many philosophers and semanticians who try to adapt Fregean semantics to natural languages.”

This is the problem Kripke has with using the natural language term "water" and trying to call it identical with the scientific term "H2O". His only choice is to massage that vague term "water" into a precise term like "H2O" to fit in with his domain of logic. Chemistry sort of does that by applying the chemical naming convention by calling H2O, "dihydrogen monoxide".

In Chomsky's "New Horizons in the Study of Language and Mind" he gives many useful examples showing this difficulty,

"Even in such usage, with its questionable invocation of natural science, we find that whether something is water depends on special human interest and concerns, again in ways understood without relevant experience; the term "impurities" covers some difficult terrain. Suppose a cup1 is filled from the tap. It is a cup of water, but if a tea bag is dipped into it, that is no longer the case. It is now a cup of tea, something different. Suppose cup2 is filled from a tap connected to a reservoir in which tea has been dumped (say, as a new kind of purifier). What is in cup2 is water, not tea, even if a chemist could not distinguish it from the present content of cup1. The cups contain the same thing from one point of view, different things from another, but in either case cup2 contains only water and cup1 only tea. In cup2, the tea is an "impurity" in Putnam's sense, in cup1 it is not, and we do not have water at all (except in the sense that milk is mostly water, or a person for the matter). If cup3 contains pure H2O into which a tea bag has been dipped, it is tea, not water, though it could have a higher concentration of H2O molecules than what comes from the tap or is drawn from the river."

The take-away: the structure of possible world semantics that Kripke set up has been used to formalise a wide variety of situations by amongst other things constructing suitable accessibility relations. Since these are dependent on the core possible world semantics, it might be good practice to make sure we understand what that is before we go off talking about these applications of that logic. — Banno

I think I understand all that. We seem (not only in this context, but in most modern discussions of logic) to have got to a situation where what logic one uses is just a function of what project one is pursuing. Logic as pragmatism. Is that grossly unfair?

In other words, if my composition of H2O and NaCl is what determines what I am referring to, then yeah, that would also determine what is meant by water. On the other hand, if what I mean by water is in some sense prior to or co-relational to the thing in the world that is being picked out, then I am not so sure that we have to use the actual-world instantiation of something when we refer. — NotAristotle

It looks as if you are saying that what determines reference is simply a question of how each speaker is using the word. I can see a sense in which that is true. But then I want to know how it is that other people can "get" what I am referring to, given that they may or may not be using the word in the same way as the speaker.

There is no need to appeal to essences in all possible worlds to understand what the name is referring to in this example (sc. "warder" is s composed of 98% H2O and 2% NaCl). — Richard B

It does seem obvious that the way a community refers to something cannot be determined by all possible future discoveries about that substance. We have to adapt how we refer to things as we go along - future cases are determined as they crop up. It seems to me that rigid designation sweeps away all the problems in pursuit of the timeless present.

This is the problem Kripke has with using the natural language term "water" and trying to call it identical with the scientific term "H2O". His only choice is to massage that vague term "water" into a precise term like "H2O" to fit in with his domain of logic. — 'Cartesian Linguistics' - James McGilvray

That's exactly right. But I would say that "massaging" our meanings is how we manage things. Our critique ought to not to target the massaging, but the sad consequence that we end up with a misleading view of our world.

I think the real answer here is it does not matter what you say, only what we humans agree upon. — Richard B

I would agree. But we need to give more of an answer to those who think it does matter. There is what may be a side-issue, but we need to be aware that just as there are many things that humans agree on, there are also many things that they disagree on. Paradoxically, human agreements may also be the frame of human disagreements.

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. — Relativist

I agree with you. Necessitarianism does seem to sweep the concept of contingency away. So we need to show why we need it. I don't have an answer.

Actual worlds may exist or possibly exist. — RussellA

We have to be very careful about our terms here. As a result of reading this thread, I have become quite confused about what "actual" actually means (!) and how it relates to "exists" (and "real"). I don't see how actual world could only possible exist. It seems to mean something close to "exists" and like it, in that neither are, in Kant's sense, predicates. (Nor, come to think of it, is "real")

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 — Relativist

I think you misunderstand Kripke's project. It is, it seems to me, to find a way of forgetting about everything that makes a problem for the project of logic. In which, perhaps, he succeeds. Then we will ask more pragmatic questions about the project.

...every concept we have misleads intellectually by producing the illusion that something not understand is understood. — RussellA

I think that's far too strictly binary. Understanding is not a whole, but is (almost always) partial. No single concept can cater for all contexts, but they can be useful and helpful in some contexts. That is enough.

I don't see how actual world could only possible exist — Ludwig V

Yes, agreeing what a word means is problematic. Perhaps it is standard practice in philosophy that only our world is the actual world, and possible worlds cannot be called actual worlds .

It gets complicated. For the Indirect Realist, we only know the actual world as representations in the mind, whereas for the Direct Realist, we directly perceive an actual world existing independently of our representations of it.

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. — Relativist

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. — Relativist

For Kripke, that an object, an individual such as Aristotle, is the same object in all possible worlds, is a Rigid Designator, is a consequence of his Theory of Naming.

That Aristotle is the same individual is not because of any knowledge about his essence or identity, but because of a casual chain linking Aristotle back through time to being the son of his parents at the moment of his baptism.

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

That Aristotle is the same individual in different possible worlds, has the same identity and has the same essence, does not mean that Aristotle cannot be a teacher in one possible world and a carpenter in another possible world.

The individual Aristotle in all possible worlds is necessarily tied through Kripke’s Theory of Naming to his origin.

Aristotle's origin is necessary and sufficient for the identity and essence of the individual Aristotle in all possible worlds’

However, his origin is not necessary for contingent features of Aristotle, such as being a teacher or carpenter.

In standard modal logic there is exactly one actual world..........................We've a set of possible worlds, W, and we can label any one of these the actual world, w₀. — Banno

:grin: IE, it is wrong to say that there are actual possible worlds.

Importantly, accessibility is not causal, temporal, or epistemic unless specified. And it can be so specified. It constrains what worlds we have access to. — Banno

:grin: IE, there are different types of modal logic, and we always need to be clear which type we are referring to.

For the Indirect Realist, we only know the actual world as representations in the mind, .... — RussellA

Clearly, I'm not a indirect realist, because I don't accept that we only know the actual world as representations in the mind, because, as Berkeley pointed out, unless you can compare a representation with its original, you can't establish what, if anything, it is a representation of.

...whereas for the Direct Realist, we directly perceive an actual world existing independently of our representations of it. — RussellA

Clearly, I'm not a Direct Realist because I don't accept that we directly perceive an actual world existing independently of our representations of it.

I don't think that "directly" and "indirectly" are applicable in this context and I have my doubts about "real", because "unreal" in this context does not have a clear meaning.

That Aristotle is the same individual is not because of any knowledge about his essence or identity, but because of a casual chain linking Aristotle back through time to being the son of his parents at the moment of his baptism. — RussellA

The implication is that the existence of the causal chain is necessary and sufficient, presumably whether or not we know it. That's extremely hard to understand, because it suggests that we do not necessarily know who Aristotle is, if anyone.

IE, it is wrong to say that there are actual possible worlds. — RussellA

I would agree with you if you mean that the idea of a possible possible world is incoherent. But all possible worlds are possible actual worlds. When we designate one of them, we are making that possibility actual. We do not make the possible world vanish and an exactly similar, but numerically different actual world appear.
The candidates in an election are all possible office-holders. When one of them wins, that very same possible office-holder becomes an actual office-holder. It is very confusing to think of that office-holder as an actual possible office-holder, but very easy to think of that actual office-holder as an erstwhile possible office-holder.

as Berkeley pointed out, unless you can compare a representation with its original, you can't establish what, if anything, it is a representation of. — Ludwig V

True. But in our daily lives we don’t need to know what the representation is of, all we need to know is the representation.

The SEP article Possible Worlds writes “The idea of possible worlds is evocative and appealing.”

Sometimes in our daily lives we need to imagine possible worlds, and sometimes we only need to know the actual world.

For example, I perceive the colour red but believe that the colour red does not exist in a mind-independent world. Something else may exist, for example a wavelength of 700nm.

When driving and I see a red traffic light, All I need to know is that I perceive the colour red in order to stop my car. It is immaterial to me what really exists in a mind-independent world. Possibly a wavelength of 700nm exists, possibly something else. In this situation, I don’t need to know a possible world of reality, all I need to know is the actual world of representations.

As you say “It is immaterial what really exactly exists in a mind-independent world because "unreal" in this context does not have a clear meaning.”
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The implication is that the existence of the causal chain is necessary and sufficient, presumably whether or not we know it. That's extremely hard to understand, because it suggests that we do not necessarily know who Aristotle is, if anyone. — Ludwig V

Perhaps this is a similar situation to Kripke’s argument for the necessary a posteriori. Water is necessarily H20 even before anyone knew that this was the case.

Aristotle is necessarily Aristotle even if no one knows it. An instance of necessary a posteriori.
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But all possible worlds are possible actual worlds. — Ludwig V

I agree, as this seems to follow what @Banno wrote:

In standard modal logic there is exactly one actual world………………………We've a set of possible worlds, W, and we can label any one of these the actual world, w₀.