# 非单调逻辑

> 【EN】Non-monotonic logic ( NML ) is a family of formal logics designed to model and better understand defeasible reasoning . Reasoners draw conclusions in a defeasible manner when they retain the right to retract these inferences upon the acquisition of further information. Numerous instances can be found, ranging from inductive generalizations to reasoning based on the best explanation, as well as inferences grounded on expert opinion. Defeasible inferences are prevalent in everyday reasoning, expert reasoning such as medical diagnosis, and scientific reasoning. Defeasible reasoning can follow complex patterns, patterns that elude classical logic (CL), intuitionistic logic (IL), or other monotonic logics that characterize deductive reasoning. Monotonic logics are not designed for and therefore do not allow for a retraction of inferences. … 【中】非单调逻辑是一族用于刻画可废止推理的形式逻辑。推理者以可废止的方式下结论，即保留在获得新信息后撤回推断的权利，归纳概括、最佳说明推理都属此类，广泛见于日常推理与医学诊断。词条讨论可废止推理的动态、冲突消解、未解决冲突下的推理，以及封闭世界假设、继承网络、基于论证的进路与缺省逻辑等形式化方案。

- ID: m13251
- 分类: structure
- 领域: 逻辑学

## 定义

非单调逻辑是一族为可废止推理建模并加深理解的形式逻辑。所谓可废止，指推理者下结论时保留在获得进一步信息后撤回该推断的权利，归纳概括、最佳说明推理、依据专家意见的推断都属此类。 脚手架作用：- 缺省跳跃：在信息不足时按常态先得出结论，避免停滞 - 例外撤回：预设结论可被反例废止，始终保留修正空间 - 优先级排序：冲突时按信息可靠程度决定保留哪条推断

## 机制

经典逻辑是单调的：前提增加，结论只会增多不会减少。常识推理却不然——由“鸟会飞”推出某个体会飞，一旦得知它是企鹅就必须撤回。非单调逻辑用缺省规则、例外条件与优先序编码这种跳跃：先按缺省得出结论，出现更高优先级的相反信息时再废止它。

## 练习

1) 分清哪些结论是缺省推出的、哪些是确定推出的；2) 列出可能的例外与冲突来源；3) 为冲突规则设定优先级或采取怀疑策略；4) 新信息到达时重新计算，确认哪些结论被废止。

## 脚手架用法

- 缺省跳跃：在信息不足时按常态先得出结论，避免停滞 - 例外撤回：预设结论可被反例废止，始终保留修正空间 - 优先级排序：冲突时按信息可靠程度决定保留哪条推断

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