What is the negation of a universal affirmative proposition?

• A. Some S are not P
• B. No S are P
• C. Some S are P
• D. All S are P

Answer: (A)

To negate a universal affirmative, you show a counterexample. A universal affirmative claims that every member of the subject class S is in the predicate class P. Its negation says there is at least one S that is not P. In standard form, that is “Some S are not P.” This directly expresses the existence of a counterexample to the universal claim, which is exactly what negation requires. The other forms do not capture that counterexample: “No S are P” would negate a different kind of statement, and “Some S are P” is an existential affirmative that does not dispute that all S are P, while the original universal statement is “All S are P.” Therefore, the correct negation is “Some S are not P.”