Case 1: One poet calls a man courageous; another describes him as fearless in battle. Their subject overlaps, but this does not prove copying of a particular verse.
Case 2: Two poems speak of a patron's generosity. Their aims coincide, but their expression may be independently composed.
Case 3: Two poems praise beauty. The general attribute is not itself a rare literary invention.
Agreement in the subject and agreement in a particular imaginative representation must not be treated as identical.