Although couplets are the evolution of poetic forms, there are only upper couplets and lower couplets, and the number of words is not fixed. They can be as long as two or three words, dozens, dozens of crosses or even hundreds of words. Poetry, aphorisms, aphorisms, proverbs and even vernacular Chinese can all become couplets, which are rich in content. The cross-comments closely related to couplets can be said to be the theme of couplets, which can highlight the core significance and play the role of making the finishing point in couplets.
Although couplets are an evolution form of poetry, their main function is hanging and posting, so their contents must be presented in the form of calligraphy. Therefore, under the concrete expression of China's calligraphy, the antithetical couplets are visual and auditory, abstract and concrete, or vigorous and elegant, which makes their books and articles complement each other and their artistic interests blend well, and become a unique art form of literature and learning in China. Throughout the ages, literati are happy to write couplets as a reward. They will hang couplets on the wall, taste the good rhyme between chanting and feel the beautiful words in calligraphy, which makes people fondle it.