Which fallacy occurs when the middle term is not distributed at least once?

• A. Undistributed Middle
• B. Illicit Major
• C. Exclusive Premises
• D. Drawing a Negative Conclusion

Answer: (A)

The middle term must be distributed at least once in a syllogism so it properly links the subject and the predicate; without that distribution, the argument can’t guarantee a real connection between the two extremes. For example, consider these premises: all dogs are animals, and all cats are animals. From these, it would be invalid to conclude that all dogs are cats. The middle term here is animals, and it isn’t distributed in either premise. Both statements simply place dogs and cats inside the broad group of animals, but they don’t show that the entire dog group overlaps with the entire cat group. Because the middle term hasn’t been distributed, there’s no guaranteed link between dogs and cats, so the conclusion doesn’t follow. This is the undistributed middle.

Other options describe different logical issues (like distributing the major term in the conclusion, or premises being both negative, or drawing a negative conclusion from affirmative premises) and don’t address the specific problem of the middle term’s lack of distribution.