※ 引述《realove (realove)》之铭言： : 你问这个问题还蛮有趣滴 : 我不知道I会怎麽回答 但ㄟ : 我说一下我个人的意见 : 我想I之前 就有强调两种意义的possible world : 一种是david lewis讲的possible world : (我对lewis没有很熟 讲错了请纠正) : 这种possible world的集合 包括了actual world Yes, and Lewis said all possible worlds (all members in W) are concrete. : 另一种是kripke讲的possible world : 这种意义下的possible world是相对於actual world而言 它实际上不存在 却有可能存在 : 如假如有一个世界的状态是 Aristotle不是柏拉图的学生 那这只是一个可以被想像的 : (conceivalbe)possible world 而不是actual world : 所以对kripke而言 possible world的集合里并不包括actual world No, Kripke semantics says nothing about actual world. and there is no outstanding reason suppose actual world is different from other possible worlds semantically, since we can handle all relevant issues in modal logic. Simplification is one of our concerns. I will show you, if actual world is different from other possible worlds, then its model will look like what. Suppose I can do that. Model-theoratically, If Kripke supposed actual world is not in W, there will be a serious problem in the original model. The problem is that we get some objects the model cant handle. The original Kripke's model have to be modified. Intutively, we can say that actual world (wa) itself is a set , and has its own relations, so that our new model for wa becomes <Wa,Ra,v> , called Mwa. But soon we encounter a crux, since wa is different from its friends - others possible world. Between them, there must have at least a relation(?) between them, or we cant draw a clear line to specify them. Models for other possible worlds would be <Wo,Ro,v>, called Mom. The most important target now is try to find the diagram between Mom & Mwa, so that we can get a "good" semantics for this topic. Forgive my ignorance and foolish, the easiest way is to say this diagram is isomorphic. For a reson(not quiet strickly), its very unwisdom to divde similar realtions into Ro and Ra. Now we have a new model functions as K, very likely in practice. So, we use the orignal K-semantics again. Something tricky, isnt it? --

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