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1. • CommentRowNumber1.
   • CommentAuthorTim_Porter
   • CommentTimeOct 19th 2010
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   Author: Tim_Porter
   Format: MarkdownItexI found in one of the modal logic sources the following Necessity = truth in all possible worlds Possibility = truth in some possible world. Discuss. :-)

   I found in one of the modal logic sources the following

   Necessity = truth in all possible worlds

   Possibility = truth in some possible world.

   Discuss. :-)

2. • CommentRowNumber2.
   • CommentAuthorTodd_Trimble
   • CommentTimeOct 20th 2010
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   Author: Todd_Trimble
   Format: MarkdownItexYes, this would be a good thing to discuss, for example in conjunction with Awodey-Kinisha. Hopefully soon!

   Yes, this would be a good thing to discuss, for example in conjunction with Awodey-Kinisha. Hopefully soon!

3. • CommentRowNumber3.
   • CommentAuthorUlrik
   • CommentTimeOct 20th 2010
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   Author: Ulrik
   Format: MarkdownItexYou're thinking it looks circular? Well, doesn't it go like this? Necessity = truth in all possible worlds, Contingency = truth in some possible world. As for what is a possible world, that's another question. A possible (:-)) answer begins: "Consider a Kripke model $(W,R,\Vdash)$..."

   You’re thinking it looks circular? Well, doesn’t it go like this?

   Necessity = truth in all possible worlds,

   Contingency = truth in some possible world.

   As for what is a possible world, that’s another question. A possible (:-)) answer begins: “Consider a Kripke model $(W,R,\Vdash)$…”

4. • CommentRowNumber4.
   • CommentAuthorTobyBartels
   • CommentTimeOct 21st 2010
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   Author: TobyBartels
   Format: MarkdownItexI never understand how this was supposed to make sense of sentences like $\diamond \square p$. Even $\diamond p \Rightarrow p$ seems like a type mismatch to me. I mean, I can read about and understand modal logics. It just has nothing to do with my intuition about alternative worlds. @ Urs: No, contingency = truth in some possible world but not in all possible worlds. That is, it's contingent iff it's possible but unnecessary.

   I never understand how this was supposed to make sense of sentences like $\diamond \square p$. Even $\diamond p \Rightarrow p$ seems like a type mismatch to me.

   I mean, I can read about and understand modal logics. It just has nothing to do with my intuition about alternative worlds.

   @ Urs:

   No, contingency = truth in some possible world but not in all possible worlds. That is, it’s contingent iff it’s possible but unnecessary.

5. • CommentRowNumber5.
   • CommentAuthorTim_Porter
   • CommentTimeOct 21st 2010
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   Author: Tim_Porter
   Format: MarkdownItexMy understanding, such as it is came, by looking at multiagent systems and the Muddy Children problem. To start with in that problem there are loots of worlds that may be possible but as the recursion happens this narrows down, but in a subtle non=deterministic way. Understanding that argument is very hard I think. The action on the models of the recursion seems to me to require a lot more study than is usually given to it in books.

   My understanding, such as it is came, by looking at multiagent systems and the Muddy Children problem. To start with in that problem there are loots of worlds that may be possible but as the recursion happens this narrows down, but in a subtle non=deterministic way. Understanding that argument is very hard I think. The action on the models of the recursion seems to me to require a lot more study than is usually given to it in books.