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Barcan Formula

Shawn December 18, 2018 at 02:29 5500 views 11 comments
I'm interested if anyone knows of any interpretations of the Barcan Formula.

My intuition tells me that actualism is the right theory of Quantified Modal Logic. It seems like a perfect balance for applying Occam's Razor to possible world semantics.

Just as a preliminary, if anyone is interested to see:

https://math.berkeley.edu/~buehler/First-Order%20Modal%20Logic.pdf

The domain or framing condition for any set of counterfactuals is intuitively linked to the actual world, and there's no room for ascertaining the truth of necessary conditionals in other possible worlds. And, if so then what criteria would one need to judge the merit of a necessary condition in another possible world? It's hopelessly inchoate or self-refuting!

Thoughts and criticism welcome.

Comments (11)

Snakes Alive December 18, 2018 at 04:29 #238389
I'm not following. What does this have to do with the Barcan formulas?

In your standard modal semantics, all formulae are evaluated with respect to a possible world. This will include conditional or counterfactual formulae, however you translate or interpret them. Actualism about modality isn't a position affecting the modal logic per se. It's a metaphysical position, so when you're committing to using a modal logic, it becomes an interpretation of the metaphysical commitments of that logic.
Shawn December 18, 2018 at 17:57 #238511
Quoting Snakes Alive
What does this have to do with the Barcan formulas?


The Wikipedia entry on the Barcan formula states:

Quoting Wiki
The Barcan formula has generated some controversy because—in terms of possible world semantics—it implies that all objects which exist in any possible world (accessible to the actual world) exist in the actual world, i.e. that domains cannot grow when one moves to accessible worlds. This thesis is sometimes known as actualism—i.e. that there are no merely possible individuals. There is some debate as to the informal interpretation of the Barcan formula and its converse.


Therefore, if we are limited to the actual world when positing counterfactuals, then how are necessary conditionals possible to stipulate for other possible worlds?

Quoting Snakes Alive
In your standard modal semantics, all formulae are evaluated with respect to a possible world.


You mean, that all formulae are evaluated with respect to the actual world?

Deleted User December 18, 2018 at 18:26 #238520
This user has been deleted and all their posts removed.
Shawn December 18, 2018 at 18:29 #238521
Quoting tim wood
Question: Are not all worlds accessible to the actual world part of, or in or attached to, the actual world? If yes, then "possible" worlds are actually impossible worlds. If no, then the implication is denied. Yes?


Yes, but, I don't see how a possible world can be determined as impossible? It merely states that the state of affairs of a possible world is always going to be dependent on our own. Counterfactuals can only exist wrt. to events in the actual world and cannot be quantified beyond that. This is what actualism in philosophy asserts to the best of my knowledge.
Deleted User December 18, 2018 at 20:02 #238578
This user has been deleted and all their posts removed.
Shawn December 18, 2018 at 20:11 #238581
Quoting tim wood
That takes in a lot of ground. It leaves only im-possible worlds outside the actual world.


Well, there can exist an infinite amount of possible worlds, just originating from this one. But, I think the word "real" needs to be dropped into the discussion here. What is a "real" world? One where our set of circumstances have dictated its evolution?
Shawn December 18, 2018 at 21:01 #238599
@andrewk, what do you think about all this?
Snakes Alive December 19, 2018 at 01:54 #238670
Quoting Wallows
You mean, that all formulae are evaluated with respect to the actual world?


No.
Shawn December 19, 2018 at 14:41 #238750
Reply to Snakes Alive

What do you mean?
Shawn May 28, 2019 at 00:30 #292725
Sorry to necromance an old thread, mods...

I am feeling audacious and have a nagging interest in utilizing the Barcan formula to prove the coherence of the thought that within a possible world scenario, there can only be a finite amount of possible worlds given that entities (a priori) cannot be multiplied into existence. I know this smells of essentialism given the ambiguity surrounding the definition of what constitutes an entity; but, if we expand the scope to the sum total of possible worlds, then God is the only entity that can be stipulated to inhabit every possible world, leading to a solipsistic conclusion that either God inhabits every possible world or the ineffable assertion that s/he/it transcends it.

Thoughts?
Shawn June 12, 2019 at 21:34 #297053
There was a question posted on StackExchange about this issue. I'm just sharing what the Barcan Formula is all about:

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