Which of the following is a Terminological Rule of validity for categorical syllogisms?

• A. There must be four terms
• B. The middle term must occur in the conclusion
• C. There must be three and only three terms
• D. The major term must be undistributed in the premises

Answer: (D)

In categorical syllogisms, how the terms are distributed across the premises and conclusion matters. This falls under a terminological rule that safeguards valid inferences by controlling how much of a class we’re talking about in each part of the argument.

The statement about the major term being undistributed in the premises is a classic guard against the illicit major fallacy. If the major term were distributed in any premise, you’d be projecting a claim about all members of that class into the premises, and that overreach can lead to an invalid conclusion. By requiring the major term to be undistributed in the premises, you’re ensuring that you’re not generalizing too much from the premises to the conclusion.

The other possibilities miss the intended rule: one is false because a syllogism does not require four terms, another is false because the middle term does not appear in the conclusion, and while having exactly three terms is a real structural feature, the option focusing on the major term’s distribution directly captures a standard terminological constraint that preserves validity.