Fallacy of The Undistributed Middle
The fallacy of the undistributed middle is a fallacy that is committed when the middle term in a categorical syllogism is not distributed. It is thus a syllogistic fallacy. More specifically it is also a form of non sequitur.
The fallacy of the undistributed middle takes the following form:
- All Zs are Bs.
- Y is a B.
- Therefore, Y is a Z.
It may or may not be the case that "all Zs are Bs," but in either case it is irrelevant to the conclusion. What is relevant to the conclusion is whether it is true that "all Bs are Zs," which is ignored in the argument.
Note that if the terms were swapped around in the first co-premise then it would no longer be a fallacy, although it could still be unsound. This also holds for the following two fallacies which are similar in nature to the fallacy of the undistributed middle and also non sequiturs.
An example can be given as follows:
- All men are humans.
- Mary is human.
- Therefore, Mary is a man.
Read more about this topic: Non Sequitur (logic)
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