In a standard-form categorical syllogism, which of the following rules must be satisfied for the syllogism to be valid?
Correct: A
The fundamental rule of categorical syllogisms is that the middle term must be distributed at least once. If the middle term is not distributed in either premise, the fallacy of the undistributed middle occurs and the syllogism is invalid. The middle term need not be distributed in both premises. Distribution of the major and minor terms in the conclusion is not always required — only the middle term distribution rule is mandatory for validity.