Affirmative Conclusion from a Negative Premiss
Type: Syllogistic FallacyForm:
Any form of categorical syllogism with an affirmative conclusion and at least one negative premiss.
| Example | Counter-Example |
|---|---|
| All judges are politicians.
Some lawyers are not judges. Therefore, some lawyers are politicians. |
All whales are mammals.
Some fish are not whales. Therefore, some fish are mammals. |
Venn Diagram:
This diagram represents both the Example and Counter-Example, and shows that neither is valid, since the conclusion, "Some S is P", is not shown to be true.
Syllogistic Rule Violated:
All validating forms of categorical syllogism which have one negative premiss also have a negative conclusion.
Source:
Irving Copi & Carl Cohen, Introduction to Logic (10th Edition), (Prentice Hall, 1998), pp. 277-8.
