Why must the Seven Rhymes be opposed?

Duality is an important rhetorical format in ancient poetry, which existed in pre-Qin poetry, and embodies the characteristics of balanced beauty in poetry. Antithesis is an important symbol that distinguishes it from quatrains in regular poetry. It requires antithesis of couplets (three or four sentences) and necklaces (five or six sentences), so that the parts of speech of the corresponding words are the same or similar, and occasionally opposite. When writing metrical poems, there are several situations in which antithesis is not strict, such as different parts of speech, even words, too dry antithesis and so on.