According to the Third Law of Opposition, which of the following is true about subcontraries?

• A. They may both be true.
• B. They must have the same truth value.
• C. They may both be true, but cannot both be false.
• D. If one is true, the other must be false.

Answer: (C)

Subcontraries are the pair of particular propositions about the same subject term, namely “Some S are P” and “Some S are not P.” They can both be true if there are some S that are P and some S that are not P, so the predicates split the existing S into both categories. But they cannot both be false when we assume the subject class exists, because with at least one S, it’s possible for at least one of the two statements to be true (and in fact both can be true if there are some S that are P and some that are not P). So the best description is that they may both be true, but cannot both be false. For example, some artists are rich and some artists are not rich can both hold true.