Fallacy of exclusive premises

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:

Since no mammals are fish and some fish are not whales, it follows that some whales are not mammals.
This article was originally based on material from the Free On-line Dictionary of Computing, which is licensed under the GFDL.

See also: Fallacy of exclusive premises, Categorical syllogism, Free On-line Dictionary of Computing, GNU Free Documentation License, Logical fallacy, Validity