In a syllogism, if the middle term is not distributed at least once, which fallacy is involved?

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

Answer: (A)

In this type of reasoning, how we treat the middle term matters because it shows whether the argument truly links the two extremes. The middle term is the one that appears in both premises but not in the conclusion, and distribution means we’re speaking about all members of a class when we say something about a term. If the middle term is not distributed in either premise, we don’t have a solid bridge from one extreme to the other. For example, consider All S are M and All P are M. Here the middle term M is the predicate in both premises and is not distributed, so from these premises you cannot validly conclude that All S are P. This misstep is the undistributed middle fallacy. The other listed fallacies involve different distribution issues or forms of invalid inference—illicit major comes from distributing the major term in the conclusion without distributing it in the premises, exclusive premises involve both premises being negative, and drawing a negative conclusion concerns the relationship between the premises and the conclusion in terms of negativity.