Fallacy of exclusive premises

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The fallacy of exclusive premises is a formal fallacy committed in a categorical syllogism that is invalid because both of its premises are negative.

Example:

No mammals are fish.
Some fish are not whales.
Therefore, some whales are not mammals.

It is a syllogistic fallacy.

This article was originally based on material from the Free On-line Dictionary of Computing, which is licensed under the GFDL.
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