Undistributed middle:

Formal Fallacy

Definition	Example
When the middle general term in a categorical syllogism is not distributed to more specific terms of the same category.	All humans are 2-legged, and all birds are 2-legged. Therefore all humans are birds.
Notes
In the example, the conclusion does not follow since it is 2-leggedness that is the larger more general category, encompassing both humans and birds, without either one of the smaller more specific categories encompassing the other. If one of the premises instead stated that all 2-legged things are birds, then the argument would be valid (but not sound).

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Case Study One

Young people looking for social acceptance might argue to themselves “The cool wear sunglasses, and I’m wearing sunglasses. Therefore I’m one of the cool.”

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Case Study Two

“All vampires are imaginary, and all gods are imaginary, so all vampires are gods.”

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^{Keep in mind that a fallacious argument does not entail an erroneous position.}

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