Which is a major test for validity in the four-rule system?

• A. Ensure the middle term is distributed; ensure no illicit major/minor; ensure distributed terms in the conclusion are distributed in premises; ensure no two negative premises.
• B. Ensure all premises are affirmative.
• C. Ensure the conclusion is distributive.
• D. Ensure there are exactly two premises and one conclusion.

Answer: (A)

Validity in the four-rule syllogistic is checked against a standard set of four constraints on how terms are distributed and how premises relate to the conclusion. The main test here is that:

• The middle term must be distributed at least once in the premises, so the two ends can be properly linked.

• You cannot illicitly distribute the major or minor term in the conclusion; if the major or minor term is distributed in the conclusion, it must also be distributed in its corresponding premise.

• Any term that is distributed in the conclusion must be distributed in at least one premise.

• There cannot be two negative premises, since that eliminates any valid connection between the terms.

This combination precisely captures what makes a syllogism valid in the four-rule system. The other options miss one or more of these essential safeguards: you don’t have to require all premises to be affirmative, the conclusion’s distribution isn’t the sole determiner of validity, and the exact two-premise structure alone doesn’t ensure validity.