为提高学习效率就得掌握换位推理必须遵循的规则
To improve learning efficiency, one must master the rules that must be followed in conversion reasoning.
李宏 湖北省十堰市郧阳中学
Li Hong Yunyang High School, Shiyan City, Hubei Province
换位推理（换位法）的三条核心规则，不仅是形式逻辑的基础推理法则，更是打通高中各学科知识壁垒、深化概念理解、培养逻辑思维的工具。
The three core rules of Conversion Reasoning (Conversion Method) are not only the basic inference rules of formal logic, but also a tool to break down the knowledge barriers between various senior high school subjects, deepen the understanding of concepts, and cultivate logical thinking.
展开剩余88%换位推理（换位法）必须遵循的规则:
Rules for Conversion Inference (Conversion Method):
（从所给真实前提得出真实结论必须遵循的规则
Rules that must be followed to derive a true conclusion from given true premises）
一、保持联项不变（肯定↔肯定；否定↔否定）
规则：前提的质（肯定/否定）换位后在结论中保持不变。
Preserve the copula (affirmative↔affirmative; negative↔negative):
The quality of the premise remains unchanged in the conclusion.
示例：
Example:
肯定前提：“所有金属都是导体” → 肯定结论：“有些导体是金属”。
Affirmative premise: "All metals are conductors" → Affirmative conclusion: "Some conductors are metals" .
否定前提：“没有昆虫是哺乳动物” → 否定结论：“没有哺乳动物是昆虫”。
Negative premise: "No insects are mammals"→Negative conclusion: "No mammals are insects" .
二、互换主项与谓项的位置
规则：前提的主项在结论中变为谓项，前提的谓项在结论中变为主项。
Swap the positions of subject and predicate terms:
The subject of the premise becomes the predicate in the conclusion, and vice versa.
示例：前提：“所有 S 是 P”→ 结论：“有些 P 是 S ”。
Example:Premise: "All S are P" → Conclusion: "Some P are S" .
注：全称肯定命题（如“所有 S 是 P”）换位后需降级为特称肯定命题（“有些 P 是 S”），否则违反周延规则。
Note: When converting a universal affirmative proposition (e.g., "All S are P"), it must be downgraded to a particular affirmative proposition ("Some P are S"), otherwise the rule of distribution is violated.
三、周延性规则：结论中不得扩大项的周延性
No term may gain distribution in the conclusion:
规则：
前提中不周延的项 → 换位后结论中不得周延；
If a term is undistributed in the premise, it must remain undistributed in the conclusion.
前提中周延的项 → 结论中可周延可不周延。
A term that is distributed in the premise may or may not be distributed in the conclusion.
结论中周延的项，前提中与之对应的项一定要周延；
Terms distributed in the conclusion must correspond to distributed terms in the premise;
在结论中不周延的项，在前提中可以对应周延的项，也可以对应不周延的项。
Terms undistributed in the conclusion may correspond to either distributed or undistributed terms in the premise.
关键限制：若前提中不周延的项在结论中周延，则推理无效。
Critical implication:Invalid conversion occurs if an undistributed term becomes distributed .
如将“所有 S 是 P”换位为“所有 P 是 S”即违反规则３---因“P”在前提中不周延，在结论中却变为周延项。
e.g., converting "All S are P" to "All P are S" violates Rule ３ since "P" is undistributed in the premise but distributed in the conclusion.
有效换位：“所有 S 不是 P” → “所有 P 不是 S”
Valid conversion: "All S are not P" → "All P are not S"
原因：否定命题的谓项“P” 在前提中周延，结论中仍周延，符合规则３。
Reason: The predicate term "P" remains distributed in both premise and conclusion, complying with Rule
四、不同命题类型的换位规则有效性
Validity of Conversion Rules by Proposition Type
①全称肯定（A）
Universal Affirmative (A)
所有 S 是 P→有些 P 是 S（降级）
All S are P→Some S are not P
“所有马是动物”→“有些动物是马”
“All horses are animals” → “Some animals are horses”
②全称否定（E）
Universal Negative (E)
所有 S 不是 P→所有 P 不是 S（直接换）
No S are P→No P are S (direct conversion)
“没有鸟是哺乳动物”→“没有哺乳动物是鸟”
“No birds are mammals” → “No mammals are birds”
③特称肯定（I）
Particular Affirmative (I)
有些 S 是 P→有些 P 是 S（直接换）
Some S are P→Some P are S (direct conversion)
“有些学生是党员”→“有些党员是学生”
“Some students are Party members” → “Some Party members are students”
④特称否定（O）
Particular Negative (O)
有些 S 不是 P→不可换位
Some S are not P→Cannot be converted
“有些人不是演员” ↛“有些演员不是人”（无效！）
“Some people are not actors” ↛ “Some actors are not people”" (Invalid!)
五、特称否定命题（O）为何不可换位？
Why the Particular Negative Proposition (O) Cannot Be Converted?
前提中主项 “S”（如“人”）不周延（特称主项），但换位后作为否定命题的谓项（如“演员不是人”中的“人”）必然周延，违反规则3(任何项在结论中不得获得周延性)。
In the premise, the subject "S" (e.g., "people") is undistributed (as the subject of a particular proposition), but after conversion, it becomes the predicate of a negative proposition (e.g., "people" in "Some actors are not people"), where it must be distributed. This violatesRule 3 (no term may gain distribution in the conclusion)
教材内容是对客观世界精确、系统化的逻辑陈述，其本身就是一个严谨的知识体系。
Textbook content consists of accurate and systematic logical statements about the objective world, and it is inherently a rigorous knowledge system.
在高考有限的时间内，换位推理提供了一种快速验证选项或结论有效性的思维工具。
Within the limited time of the college entrance examination, conversion reasoning serves as a thinking tool for quickly verifying the validity of options or conclusions.
能帮助我们更深刻、更准确地理解这个体系的内在结构，避免学习中的常见思维误区，从而实现高效学习。
It enables us to understand the internal structure of this system in a deeper and more accurate manner, avoid common thinking fallacies in learning, and thereby achieve efficient learning.
Explorer of Innovative Thinking
Author: Li Hong
Yunyang High School, Shiyan City, Hubei Province
January 1, 2026
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