# 可能世界

> 【EN】Anne is working at her desk. While she is directly aware only of her immediate situation — her being seated in front of her computer, the music playing in the background, the sound of her husband's voice on the phone in the next room, and so on — she is quite certain that this situation is only part of a series of increasingly more inclusive, albeit less immediate, situations: the situation in her house as a whole, the one in her neighborhood, the city she lives in, the state, the North American continent, the Earth, the solar system, the galaxy, and so on. On the face of it, anyway, it seems quite reasonable to believe that this series has a limit , that is, that there is a maximally inclusive situation encompassing all others: things, as a whole or, more succinctly, the actual world . Most of us also believe that things, as a whole, needn't have been just as they are. … 【中】词条以内嵌情境为引：我们对自己直接情境的意识，只是层层更大情境中的一环。类比之下，现实世界被看作众多可能世界之一。文中讨论可能世界在模态逻辑中的作用，包括它如何失去又重新获得外延性、如何刻画现实性、丰富性与重组原则，并比较具体论与抽象论各自的优劣。

- ID: m13279
- 分类: structure
- 领域: 逻辑学

## 定义

可能世界是模态逻辑与形而上学的核心工具：把必然、可能、偶然解释为在全部或某些可能世界中的真值。争论在于可能世界是什么，是像我们世界一样的具体宇宙，还是抽象的最大一致事态或命题集合。 脚手架作用：- 模态换算：把必然与可能译成对世界域的量词，化模态推理为量化推理。 - 反事实推演：构造最接近现实的替代世界，检验因果与依赖关系。

## 机制

可能世界的有效性来自语义学：把模态算子解释为对世界域的量词之后，必然真理即在所有可及世界中为真，可能真理即在某个可及世界中为真。可及关系的结构决定了模态系统的强弱，由此把原本晦涩的模态推理转化为一阶量化推理。

## 练习

1) 把待判定的模态命题翻译成在所有或部分世界中为真；2) 明确所论世界域的范围与可及关系；3) 在模型上检验该命题是否成立；4) 若结论依赖具体论或抽象论，检验换一种立场是否会改变结果。

## 脚手架用法

- 模态换算：把必然与可能译成对世界域的量词，化模态推理为量化推理。 - 反事实推演：构造最接近现实的替代世界，检验因果与依赖关系。

[阅读网页](https://thinkingmodels.site/entries/detail/m13279)