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Fallacy of exclusive premises

A syllogism with of two negative premises has no valid conclusion.

For example :

No polygon is a circle.
No rectangle is a circle.

No rectangle is a polygon.

Description

Negative statements have much less descriptive power than positive ones – we learn less about A from the statement “A is not a tree” than from the statement “A is a house”. Therefore, there are a number of restrictions on what can be done with negative statements.

Even with only a single negative premise it is no longer possible to draw any positive conclusion ( affirmative conclusion from a negative premise).

If both premises are negative, there are no ways in which the middle term can reliably connect the statements. Therefore, it is not possible to infer a conclusion which connects the major and minor terms. In other words: it is not possible to draw a conclusion.

See also

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