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Four Terms
Disciplines > Argument > Fallacies > Four Terms
Description | Discussion | Example | See also
Description
All A are B. All C are D. So All A are D.
Make two statements and make an unspoken leap that connects these statements to allow a third, conclusive statement to be made.
Example
All dogs are mammals. All fish are animals. So all dogs are animals. [true, but not proven by the first two statements]
Man is an intelligent animal. No women is a man. Therefore no women are intelligent animals. ['man' has two different meanings]
Discussion
Syllogisms should have only three terms, with one term being the bridge between the major and minor premise that forms the conclusion. So where four terms appear in the major and minor premises, these two statements are logically disconnected and no logical conclusion may be drawn.
Sometimes it may appear that there are three terms (as in the second example above). Where one term actually has different meanings (equivocation) in either term (thus 'man' can mean 'humanity' or 'male').
Classification
See also
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