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undistributed middle

Subject Philosophy

DOI: 10.1111/b.9781405106795.2004.x


L ogic A logical fallacy in traditional syllogistic logic, resulting from the violation of the rule that the middle term (the term that appears twice in premises) must be distributed at least once in the premises. Any syllogism that commits this error is invalid. Consider “All philosophers are persons,” and “Some persons are bad.” No conclusion follows from these two premises because “persons” in the first premise is the predicate of an affirmative proposition, and in the second is the subject of a particular proposition. Neither of them is distributed. “If in a syllogism the middle term is distributed in neither premise, we are said to have a fallacy of undistributed middle.” Keynes, Formal Logic ... log in or subscribe to read full text

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