undistributed middle

noun

Logic. a middle term of a syllogism that does not refer to its entire class in the major premise or minor premise, with the result that the syllogism is not valid.

Origin of undistributed middle

First recorded in 1820–30

Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2023

But it would be wrong; our syllogism would have a badly undistributed middle.
The World in Chains | John Mavrogordato
Moreover, not till a man's work is translated can we uncover all the unconscious cases of "undistributed middle."
Plotinos: Complete Works, v. 4 | Plotinos (Plotinus)
You have committed the fallacy of the undistributed middle term, if you care to know the proper name for it.
Mr. Isaacs | F. Marion Crawford
For, just as in Fig I., a particular premise anywhere else involves undistributed middle.
Logic | Carveth Read

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