So except for RussellA's last question here, we're ready to move on to section 2, right?

2. Three Philosophical Conceptions of Possible Worlds

It is mentioned in the SEP article, "the truth conditions for sentences exhibiting modality de re involve in addition a commitment to the meaningfulness of transworld identity". This, as I explained above, is supported ontologically by Platonism, and requires a violation of the law of identity — Metaphysician Undercover

Transworld identity can be accounted for via haecceity: the notion that there is something unanalyzable and immaterial that makes you YOU. It's comparable to a soul. This doesn't depend on Platonism; but it does depend on immaterialism.

But the thing that belongs to the predicates enumerated does not itself change. — NotAristotle

My current understanding taken from various sources:

Suppose in possible world 5 “pigs cannot fly” and in accessible possible world 6 “pigs can fly”.

Modal languages using rigid designators
There are modal languages using rigid designators, such as Modal Logic K, Kripke’s standard modal logic.

These reference the same individual in all possible worlds, in that Aristotle is Aristotle necessarily.

These exhibit de re modality because it is about the modality of the thing. For example, all cyclists are necessarily bipedalists. All swans are necessarily white. All pigs necessarily cannot fly.

In Naming and Necessity Kripke showed that names are rigid designators. Therefore the pig in different possible worlds is the same pig. It is necessarily the same pig, it has the same intension, it has the same meaning and it is the same thing. It may be that possible world 5 is the Earth where pigs cannot fly, and possible world 6 may be Mars where there a low gravity allowing pigs to fly.

Modal languages using non-rigid designators
There are also modal languages using non-rigid designators, such as Epistemic Logic (knowledge and belief) and Temporal Logic.

These can model context dependent references, such that “the current president” can change across possible worlds, in that George Washington was the president accidentally. In other worlds he could have been a soldier.

These exhibit de dicto modality because they are about the modality of the proposition. For example, it is necessary that all cyclists are bipedalists. It is necessary that all swans are white. It is necessary that all pigs cannot fly.

Russell in his 1905 essay On Denoting developed his theory of descriptions. Therefore, what a pig is is determined by its context within the world it exists. It could be that in possible world 5 a pig = {domesticated, omnivorous, mammal, cannot fly} and a pig in possible world 6 = {domesticated, omnivorous, mammal, can fly}.

Therefore, the thing that belongs to the predicate, such as “the pig”, can change dependent on which system of modal logic is used, one with rigid designators or one without.

we're ready to move on to section 2, right? — frank

:up:

I agree with most of what you said except -->

Therefore, the thing that belongs to the predicate, such as “the pig”, can change dependent on which system of modal logic is used, one with rigid designators or one without. — RussellA

So it may be that there are no rigid designators across possible worlds. In that case, we may appear to have adopted Lewis' counterpart account, wherein a pig named "Babe" in PW 5 (possible world 5) is different, but similar to, Babe in PW 6. Point is, if there are not rigid designators, then we are dealing with different "entities" across worlds. These entities can have different predicates, but like I said, the things that belong to those predicates, per each PW, will not change. If pigs can fly in PW 6, then the version of Babe that exists in PW 6 will belong to the predicate "can fly" in that PW.

A statement about pigs generally spoken of would be de dicto. A statement about this or that pig would be de re.

This thread is for a read through of two SEP articles on possibility and actuality. The articles are:

1. Possible Worlds

2. The Possibilism-Actualism Debate — frank

There is a related issue that cuts through this: contingentarianism vs necessatarianism. Contingency entails the assumption that some counterfactuals could have been actual. That may be an unwarranted assumption. Here's an excerpt from Amy Karofsky's "A Case for Necessitarianism":

"One of the most common ways to justify the belief that contingentarianism is true is by appeal to intuition …Granted, most philosophers do share the intuition that things could have been otherwise. However the mere fact that most philosophers think that things could have been different is not adequate proof that there really are ways things could have been. In fact, what may seem to be a belief about a (so-called) unactualized possibility, when carefully examined, could actually turn out to be a mere modal illusion in the sense that it is confused and incomplete thinking and more akin to a figment of the imagination than to a genuine belief.

"Michael Jubien wrote that it is intuitive and evident from ordinary thinking that there is genuine contingency in the world…'We ordinarily think of an object could have been elsewhere because we think that our physical forces acting upon it might have been different. We think a sudden gust of wind might have altered the path of a bird in flight.'

"According to Jubien, we ordinarily think that the direction of a bird’s flight is contingent because we think that the causal series that involves the physical forces could have been different; we think that a sudden gust of wind could have altered the causal series that resulted in the bird’s path. [But] the mere fact that some people think that physical forces can be different is not adequate justification for the claim that the physical forces [i.e. those in effect in a particular instance] can be different.

"Moreover, it is not even evident that we do think the way Jubien thinks we do…We might and sometimes do think that because some actual birds paths are affected by gusts of wind, it is possible that a gust of wind could affect any bird’s path. But this type of reasoning commits the existential quantification, possible instantiation fallacy. The fact that some bird’s paths are affected by wind does not entail that the direction of any particular bird’s path is contingent; it merely indicates that the actual paths of some actual birds are affected by wind. We might and sometimes do think that this bird’s path can be affected by a gust of wind because being a bird’s path is compatible with being affected by a gust of wind. But…the compatibility of abstract properties does not prove that the instantiation of a particular property is contingent. Thus, even if we think that the abstract properties are compatible, that does not mean that we think that the particular property instances are contingently instantiated. And if we do think so, our belief remains unjustified because it presupposes contingentarianism."

She provides a number of examples from the literature wherein philosophers describe events that they claim describe "obvious" cases of contingency (such as a throw of the dice, and deliberative decisions based on future "contingencies"), but points out that these reflect merely epistemic, not metaphysical possibilities. She also reviews some claims about past contingencies, all of which entail circular reasoning: we assume things "could" have been different, and then creatively imagine differences - without actually analyzing the factors that would need to differ in order for the alleged non-actualized possibility to have obtained:

"in general, any contention that an imagined situation is a consideration of a possible, but unactual state of affairs presupposes that what does not happen can, and any suggestion that thinking about the past is an encounter with an unrealized possibility rests upon the assumption that actual past events could have failed to have occurred."

I don't think "the pig" is a predicate as it appears to refer to a specific pig or individual. "Is a pig" on the other hand could be predicated of Babe as well as other pigs. Predicates appear to designate a "kind" to which individuals belong.

So it may be that there are no rigid designators across possible worlds........................These entities can have different predicates, but like I said, the things that belong to those predicates, per each PW, will not change. — NotAristotle

In possible world 5 - “Babe is a pig and pigs cannot fly”
In possible world 6 - “Babe is a pig and pigs can fly”

Assuming rigid designators, then as I understand it is true that “These entities can have different predicate, but…………………the things that belong to those predicates, per each PW, will not change”. This means that Aristotle is necessarily Aristotle in all possible worlds, and Babe is necessarily Babe in all possible worlds.

But you are saying, given non-rigid designators, it is also true that “These entities can have different predicate, but…………………the things that belong to those predicates, per each PW, will not change”. This also means that Aristotle is necessarily Aristotle in all possible worlds and Babe is necessarily Babe in all possible worlds.

But then how is modal logic using non-rigid designators different to modal logic using rigid designators?

Right so given rigid designation the extension of Aristotle is Aristotle in all PWs where Aristotle exists. The extension of "Aristotle" in PW 5 is different than the extension of Aristotle" in PW 6 because the name "Aristotle" refers to different entities if there is no rigid designation.

So the person predicated by "is a man named Aristotle" is a different individual or "entity" in each PW. This individual that has that predication does not change in that PW.

Right so given rigid designation the extension of Aristotle is Aristotle in all PWs where Aristotle exists. The extension of "Aristotle" in PW 5 is different than the extension of Aristotle" in PW 6 because the name "Aristotle" refers to different entities if there is no rigid designation....................So the person predicated by "is a man named Aristotle" is a different individual or "entity" in each PW. This individual that has that predication does not change in that PW. — NotAristotle

Rigid designation
The person in PW 5 predicated by “is a man named Aristotle” is the same person as the person in PW 6 predicated by “is a man named Aristotle”.

Non-rigid designation
I agree that the person in PW 5 predicated by “is a man named Aristotle” Is a different person to the person in PW 6 predicated by “is a man named Aristotle”

I agree that the person in PW 5 remains the same person within PW 5.

Rigid designation
The person in PW 5 predicated by “is a man named Aristotle” is the same person as the person in PW 6 predicated by “is a man named Aristotle”.

Non-rigid designation
I agree that the person in PW 5 predicated by “is a man named Aristotle” Is a different person to the person in PW 6 predicated by “is a man named Aristotle” — RussellA

Correct.