Parallelism is the most important feature of Chinese couplet, the parallel construction is a central structual principle of composition of Chinese Couplet, and a key to reading and interpretation, but synonymous parallelism is not common. Synonymous means the very same thought is repeated, at times in the very same words.
One of the synonymous parallel example is a Chinese folk song in five lines of five characters. Each line is the same except for its last character, which successively designates the five Chinese points: center, east, west, south, north.
Fishes are playing in the east/ south/west/north/centre of Lotus leaves
This kind of structure must not be adopted in composition of Chinese Couplet. Instead, antithetical parallelism is used. Antithetical requires the constitutive properties and the formal features of a couplet has to be in "yoked similarity and difference," "interpenetration and complementarity," this has to be not only semantical, but also phonlogical, grammatical, and rhythmical.
Semantical parallelism requires the content or the thought of the first line is expressed by an antithesis in the second; or is counterbalanced by a contrast in the second. Which also include the adoption of the mythological and historico-geographical allusions. These must be all separately matched and balanced.
The moon shines, water brighten, brighten
The Wind blows, grass whip, whip
On the shrunken plum tree snow makes blossoms
On the limbless tree clouds burgeon leaves
"The moon shines/The wind blows", "snow makes blossoms/clouds burgeon leaves". Theses constitutive properties are different in two lines, which contains antithetical ideas, complementing each other and contributing to the reconstruction of a complete picture of world and mind.
In Chinese couplets, the parallelism is also grammatical. Proper nouns are matched with proper nouns; common nouns with common nouns; adjectives with adjectives and verbs with verbs. In addition, the grammatical functions in the two sentences of the couplet must match, and no word in the first line can be repeated in the match.
It is not uncommon to see couplets in which every syllable exhibits a tonal contrast with respect to the corresponding syllable of the other line of the couplet. Tones are conjoined with inflected ones, and vice versa. There are five tones of each syllable(include neutral tone) in modern Chinese, they classified into two categories, 平 (ping, even) and 仄 (ze, inflected), the level tone belong to ping, any of the three non-ping tones shang, Qu, or ru fall into category ze. Every syllable has a ping or ze value opposite to the corresponding syllable in the other line. The first syllable of the first line is ping; the first syllable of the second line is therefore ze, and so on. The whole couplet is ordered in this way.Bibliography
1. Where the Lines Meet: Parallelism in Chinese and Western Literatures, Andrew H. Plaks, Poetics Today, Vol. 11, No. 3 (Autumn, 1990), pp. 523-546 (article consists of 24 pages), Published by: Duke University Press, Stable URL: http://www.jstor.org/stable/1772825
2. Comparative poetics: an intercultural essay on theories of literature By Earl Roy Miner