What is the contrapositive of 'Some S are P'?

• A. It is valid only for universal propositions
• B. It is logically equivalent to 'Some S are not P'
• C. It is identical to the contrapositive of 'All S are P'
• D. Not valid in general; particular propositions do not have a standard contrapositive

Answer: (D)

The concept being tested is that a contrapositive is a truth-preserving transformation only for statements that have an implication form or a universal categorical form. For universal propositions like “All S are P,” the contrapositive “All non-P are non-S” preserves truth; the equivalence holds in every interpretation.

But for a particular proposition like “Some S are P,” there isn’t a standard contrapositive that preserves truth across all cases. If you tried to form an opposite-and-negation statement such as “If something is not P, then it is not S,” you can easily build a model where the original is true (there exists an S that is P) while the proposed contrapositive fails (there can be some X that is not P but still S). That shows the existential nature of the original claim doesn’t support a reliable contrapositive.

So, particular propositions do not have a standard contrapositive, and the correct understanding is that the contrapositive applicability is limited to universal (and conditional) forms. This is why the best answer is that it’s not valid in general; particular propositions do not have a standard contrapositive.