Affirmative conclusion from a negative premise
Encyclopedia
Affirmative conclusion from a negative premise is a logical fallacy that is committed when a categorical syllogism has a positive conclusion, but one or two negative premises.
For example:
The only thing that can be properly inferred from these premises is that some things that are not fish cannot fly, provided that dogs exist.
Or:
This could be illustrated mathematically as
It is a fallacy because any valid forms of categorical syllogism that assert a negative premise must have a negative conclusion.
For example:
- No fish are dogs, and no dogs can fly, therefore all fish can fly.
The only thing that can be properly inferred from these premises is that some things that are not fish cannot fly, provided that dogs exist.
Or:
- We don't read that trash. People who read that trash don't appreciate real literature. Therefore, we appreciate real literature.
This could be illustrated mathematically as
- If A ⊄ B and B ⊄ C then A ⊂ C.
It is a fallacy because any valid forms of categorical syllogism that assert a negative premise must have a negative conclusion.
See also
- Negative conclusion from affirmative premisesNegative conclusion from affirmative premisesNegative conclusion from affirmative premises is a syllogistic fallacy committed when a categorical syllogism has a negative conclusion yet both premises are affirmative...
, in which a syllogism is invalid because the conclusion is negative yet the premises are affirmative - Fallacy of exclusive premisesFallacy of exclusive premisesThe fallacy of exclusive premises is a syllogistic fallacy committed in a categorical syllogism that is invalid because both of its premises are negative.Example of an EOO-4 invalid proposition:...
, in which a syllogism is invalid because both premises are negative