Couplets generally don't need to rhyme. Generally, it can be divided into poetry couplet and prose couplet, which are relatively strict and divided into large and small parts of speech.
Significance background of couplets
Every syllable in Chinese has a strong independence and has a certain length and tone. In ancient times, there were four tones: flat, rising, going and entering. Now there are four tones: rising, falling, rising and falling, which are divided into flat and falling. Flat confrontation is a contradiction. In this way, Chinese morphemes and morphemes can establish an equal, balanced and harmonious antagonistic relationship.
Couplets are mostly written in words, often written, hung or engraved on other buildings or objects. So the second level of antithesis of couplets is the so-called literal opposition. The relativity of words means that couplets are both language art and decorative art. As decorative art couplets, it requires neatness and symmetry, giving people a harmonious and symmetrical aesthetic feeling.
Chinese characters just have the conditions to achieve neat symmetry. They exist in the form of individual squares, square and uniform, occupying an equal spatial position in writing. It is readable and visible. Its square configuration has both aesthetic principles and mechanical requirements.