Affirmative conclusion from a negative premise

Incorrect application of a syllogism by deriving an affirmative (positive) conclusion from a negative premise.

For example ◈:

All squares are rectangles.

No circles are squares.

∴ All circles are rectangles.

One fundamental rule for all syllogistic and similar inferences is that if one of the premises is a negative, the conclusion can only also be a negative statement. There are no valid syllogism forms that contradict this rule. Trying to construct one is a formal fallacy.

Furthermore, if both premises are negative, no conclusion can be inferred at all (☞ Fallacy of exclusive premises).

• Fallacy of exclusive premises – when both premisses are negative.
• Negative conclusion from affirmative premises – Reversal of this form of fallacy.
• Syllogism – underlying form of inference.

• Affirmative conclusion from a negative premise on Wikipedia
• Affirmative Conclusion from a Negative Premise on Logically Fallacious