First, the form is symmetrical, second, the content is related, third, the text is concise, and fourth, the rhythm is clear. Some people call it the four beauties of couplets, namely, the beauty of architecture, symmetry, language and rhythm.
Extended data:
Precautions for couplets:
Although antithesis of couplets has something in common with poetry, it is more demanding than poetry. Couplets can be divided into wide pairs and narrow pairs. Wide pairs can only be formed if the contents of the upper and lower couplets are related, while narrow pairs should be written in strict accordance with the standards of Li Weng Dui Yun. However, in practical couplets, wide couplets are often used, while narrow couplets are rarely used, because the requirements for antithesis are too strict, which restricts people's thinking and is suspected of harming righteousness because of the text.
The level and level of couplets are basically the same as poems. The basic law of distinguishing 135 and 246 is generally applicable.