A categorical syllogism with a negative conclusion from affirmative premises is invalid. If both premises are affirmative, the conclusion cannot be negative.
Example
“All dogs are animals.
Some pets are dogs.
Therefore, some pets are not animals.”
(The negative conclusion contradicts the premises.)
Applied example (political)
“All journalists are workers. Some citizens are journalists. Therefore some citizens are not workers.” (The negation does not follow.)
Applied example (mystical)
“All believers are people. Some neighbors are believers. Therefore some neighbors are not people.” (Contradiction with affirmative premises.)
Why it is fallacious
- Affirmative premises do not allow negation.
- A negative conclusion is introduced without support.
- The logical structure breaks.
How to spot it
- Affirmative premises with a negative conclusion.
- An unjustified contrast.
- A sign change without reason.
How to respond
- Show that negation does not follow from affirmatives.
- Ask for a coherent reformulation.
- Require external evidence if negation is intended.