# The Logic of Conditionals

> 【EN】This article provides a survey of classic and recent work in conditional logic. We review the problems of a two-valued analysis and examine logics based on richer semantic frameworks that have been proposed to deal with conditional sentences of the form “if A , B ,” including trivalent semantics, possible-world semantics, premise semantics, and probabilistic semantics. We go on to examine theories of conditionals involving belief revision, and highlight recent approaches based on the idea that a conditional is assertable provided the truth of its antecedent makes a relevant difference to that of its consequent. We close with a brief discussion of systems accounting for the interaction of conditionals with modalities and speech act operators. 【中】词条综述条件句逻辑的经典与近期工作。它先考察二值分析的困难，继而检视为处理“如果 A，B”这类句子而提出的基于更丰富语义框架的逻辑，包括三值语义、可能世界语义、前提语义与概率语义，然后讨论借助信念修正的条件句理论，并着重介绍近期的思路：一个条件句可断言，当且仅当其前件的真对后件的真构成相关差异。

- ID: m13241
- Category: structure
- Domain: 逻辑学

## Definition

条件句逻辑研究“如果 A，那么 B”这类句子的推理规律。它先考察二值分析的困难，再检视基于更丰富语义框架的各种逻辑，包括三值语义、可能世界语义、前提语义与概率语义，并讨论借助信念修正的条件句理论。 脚手架作用：- 反事实推演：设想最接近现实的前件为真世界，看后件是否成立。 - 假设评估：前件为假时仍判断条件句的意义，避免空洞为真。 - 概率替换：用条件概率高低替代真值判断，处理不确定推断。

## How it works

若把条件句等同于实质蕴涵，那么只要前件为假，整个句子就为真，这不合直觉。可能世界语义的做法是比较世界：在最接近现实且前件为真的那些世界里，后件是否为真；概率语义则要求条件概率足够高。二者都能解释前件为假时条件句为何仍可有意义地为真或为假。

## Practice

1) 判断条件句是直陈的还是反事实的，前件是否实际为假；2) 若是反事实，找出最接近现实而前件为真的那些事态；3) 检查其中后件是否为真，或计算相应的条件概率；4) 若后件的变化不依赖前件，则判为假。

## Use

- 反事实推演：设想最接近现实的前件为真世界，看后件是否成立。 - 假设评估：前件为假时仍判断条件句的意义，避免空洞为真。 - 概率替换：用条件概率高低替代真值判断，处理不确定推断。

[Read the web page](https://thinkingmodels.site/en/entries/detail/m13241)