This term refers to rules and practices which create tonal and rhythmical beauty in prose and verse by blending sounds, rhythms and tones together. Zhou Yong, a scholar of the Qi and Liang periods of the Southern Dynasties, divided the intonation of the Chinese language into four tones: the level tone, the rising tone, the entering tone and the falling tone. On that basis, Shen Yue (441-513), another scholar, proposed his rules for poetry writing, whereby high pitches are countered by low ones and level and rising tones are countered by entering and falling tones. He also analyzed the eight types of poor matches between tones, initial consonants and ensuing vowels. In his representative work The Literary Mind and the Carving of Dragons, Liu Xie (465?-520) pointed out that rhythmical beauty in poetry can be created by using various tones alternately (i.e., countering even and rising tones with entering and falling tones). Likewise, beauty of echoing can be produced by adopting the same vowel at the end of each poetic line. Liu Xie extended this rule of tonal and rhythmical harmony to other genres of writing to both ensure readability and express his love for the beauty of chanting. His effort shows Southern Dynasties scholars' pursuit of the beauty of formalism, which later inspired Tang Dynasty literary figures to create neat and beautiful metrical poetry. The early theories of metrical beauty, drawing heavily from traditional musical terminology, later developed into the phonology of the Chinese language.

The five colors set each other off beautifully, and musical instruments made of eight materials produce harmonious and smooth sounds. One should make all colors and musical notes fit together nicely. Poetry, too, should vary in intonation, alternating between the even and rising tones and the entering and falling tones, and also between low and high sounds. If a tone rises gently, the tone that follows it should be loud and short. (The History of Song of the Southern Dynasties)

Metrical rules are derived from human sounds. Human sounds have naturally developed pentatonic scale. Ancient kings and emperors produced melodies and songs in imitation of human sounds. Apparently, it is musical instruments that mimic human sounds, not vice versa. Therefore, language is crucial to the expression of thought. As to suiting language to metrical rules, it is only to make verbal utterance easier. (Liu Xie: The Literary Mind and the Carving of Dragons)