Affirmative Conclusion from a Negative Premise
A formal fallacy in categorical syllogisms where the conclusion is affirmative but at least one premise is negative; valid syllogisms require a negative conclusion when a negative premise is present.
THE IDEA
Affirmative Conclusion from a Negative Premise
(also known as: illicit negative, fallacy of negative premises)
If you feel “lost” in the terminology, first identify which statements are affirmative and which are negative. The rule below concerns standard-form categorical syllogisms.
Description: The conclusion of a standard form categorical syllogism is affirmative, but at least one of the premises is negative. Any valid forms of categorical syllogisms that assert a negative premise must have a negative conclusion.
The logical form and original example arguments are missing. The surviving commentary identifies the negative premises and affirmative conclusions.
Example #1: Explanation: The original argument is absent, so its premises and conclusion cannot be checked here. The commentary identifies one or more negative premises (i.e. “no people...” and “no senior citizens...”) and we are attempting to draw a positive (affirmative) conclusion (i.e. “all people...”).
Example #2: Explanation: This is a categorical syllogism where we have a single negative premise (i.e. “no donkeys”) and we are attempting to draw a positive (affirmative) conclusion (i.e. “some asses”).
Exception: None.
When to use it
Evaluating arguments in debates or political speeches that contain categorical statements.
Analyzing logical errors in philosophical reasoning.
Teaching formal logic and identifying common mistakes in syllogistic reasoning.
Checking the validity of syllogisms in decision-making contexts, such as legal or ethical reasoning.
FROM THEORY TO EVERYDAY LIFE
In practice
People and Senior Citizens
The original argument is absent. The commentary identifies one or more negative premises (i.e. “no people...” and “no senior citizens...”) and we are attempting to draw a positive (affirmative) conclusion (i.e. “all people...”).
Donkeys and Asses
The original argument is absent. The commentary identifies a single negative premise (i.e. “no donkeys”) and we are attempting to draw a positive (affirmative) conclusion (i.e. “some asses”).
A MOMENT TO REFLECT
Put it to work.
Can you think of a real-world argument where someone draws a positive conclusion despite a negative premise?
Why is it logically invalid to have an affirmative conclusion when one premise is negative in a categorical syllogism?
How can you identify a categorical syllogism that commits the fallacy of affirmative conclusion from a negative premise?
CONTINUE THE CONVERSATION
Source texts
- Logically Fallacious - The Ultimate Collection of Over 300 Logical Fallacies