The rhythm of poetry includes three aspects: First, the level tone was first put forward by Shen Yue in the Northern and Southern Dynasties, and it was widely used in metrical poetry after the prosperous Tang Dynasty, mainly focusing on the coordination between level tone and level tone. The second is duality. In verse, especially in metrical poems, the requirement of duality is strict. There are generally sentence pairs in poetry, and there are also many sentence pairs and paragraph pairs in fu and eight-part essay. The third is rhyme, which means that rhyming words regularly appear in appropriate places (usually pause places). These three aspects all come from the characteristics of Chinese pronunciation, that is, monosyllabic morphemes are dominant and have tones. When writing poems, especially metrical poems, the use of parallelism, duality and rhyme is good and natural, which can enhance the sense of music and present the beauty of rhythm; If you don't use it well, it will give people a feeling of thankless, and even harm the meaning with words. Parallel prose from the Six Dynasties to the early Tang Dynasty is an obvious example.
To put it simply, ping means one sound, two sounds, three sounds and four sounds (also called falling sound).