Which statement expresses the distribution rule?

• A. The middle term must be distributed in at least one premise.
• B. Any term distributed in the conclusion must be distributed in at least one premise; otherwise the argument is invalid.
• C. The middle term must be distributed in both premises.
• D. All terms distributed in premises must be undistributed in the conclusion.

Answer: (B)

Distribution is about claiming something about all members of a class. In a valid syllogism, if a term is distributed in the conclusion (that is, we’re saying “all of this class” or equivalently about every member of that class), then that term must also be distributed in at least one of the premises. This is the rule that prevents drawing universal conclusions about a term without having premises that actually quantify over all of that term.

The statement that expresses this exactly says: any term distributed in the conclusion must be distributed in at least one premise; otherwise the argument is invalid. That’s why this option is the best answer: it captures the essential safeguard of syllogistic reasoning—you can’t universalize a term in the conclusion unless your premises already universalize that term.

For context, consider a classic form where the conclusion distributes both the subject and the predicate. The premises distribute those terms in the right way, so the conclusion’s distribution is justified. Other common rules — like the middle term needing distribution in at least one premise, or the idea that the middle term must be distributed in both premises — describe related structural requirements but are separate from this specific distribution principle. And it’s not correct to say that every distribution in premises must be undistributed in the conclusion, since terms can be distributed in both premises and conclusion in valid forms.