During the reign-period Yongming 永明 (482-493) of Emperor Wu 齊武帝 (r. 482-493) of the Southern Qi dynasty 南齊 (479-502), a new poetry style became popular. Its main advocates were Shen Yue 沈約 (411-513), Xie Tiao 謝朓 (464-499), Wang Rong 王融 (467-493), Zhou Yong 周顒 (d. 493) and Fan Yun 范雲 (451-503). The style was characterized by adaption of the music keys gong 宮 and shang 商 and strict differentiation of the four tone pitches level (pingsheng 平聲), rising (shangsheng 上聲), falling (quesheng 去聲), and "entering", i.e. consonantal (rusheng 入聲). Words with different rhymes and tone pitches were combined according to strict rules in order to produce a sound experience of outstanding beauty.
The theoretical background of this skill of poetry was called "theory of tonal rules" (Yongming shenglü lun 永明聲律論). It is expounded in Shen Yue's essay on the biography of the poet Xie Lingyun 謝靈運 385-433, Xie Lingyun zhuanlun 謝靈運傳論傳論, which is included in the official dynastic history Songshu 宋書 (ch. 76). Some statements are also found in one of his letters to Lu Que 陸厥 (472-499), Da Lu Que shu 答陸厥書.
Shen acknowledges that the old-style poetry of the Han 漢 (206 BCE-220 CE) and Wei 曹魏 (220-265) periods – which was still prevalent until the early 5th century – was characterized by the beauty of words and refined expressions but did not pay attention to the sound of words, even if outstanding poets like Wang Can 王粲 (177-217) and Cao Zhi 曹植 (192-232) had done so (by chance, shi zbu zhi qi suo yi ran 實不知其所以然).
This mode of poetic composition was thoroughly new in comparison to the "old-style" modes (gushi geyao 古詩歌謠) hitherto used, and the literary products were therefore also called "new-style poems" (xintishi 新體詩, xinbianti 新變體). The basic rules of Shen Yue's concept were that a "floating (flat) tone" (fusheng 浮聲) was to be followed by a "cutting (moving) sound" (qiexiang 切響); in one bamboo slip (one verse), different sounds and rhymes were expected (yinyun jin shu 音韻盡殊), and the "weight" of sounds had to be different between two verses (qingzhong xi yi 輕重悉異). The excellent poet was able to avoid certain phenomena, like "flat in the front, rising at the end (of a verse)" (ping tou shang wei 平頭上尾), "wasp waists" (fengyao 蜂腰) within a five-syllable verse (equal sound of the second and the fifth word – dearth in the middle), "crane knees" (hexi 鶴膝) in three verses (the rhyme of the first and the third identical – knobs in the middle), excessive use of "large rhymes" (dayun 大韻) or of "small rhymes" (xiaoyun 小韻), of "side knots" (pangniu 旁紐, same or similar sound but different tone pitch) or of "right knots" (zhengniu 正紐, excessive use of same or similar rhymes in one verse). Shen's theory was usually called the "Book of the four tones" (Sishengpu 四聲譜). The book catalogue Jingji zhi 經籍志 in the official dynastic history Suishu 隋書 lists a book of Shen Yue called Sisheng 四聲, with a length of one fascicle. It was lost during the Tang period 唐 (618-907).
Scholars rated Shen Yue’s system of rules differently. While Liu Xie 劉勰 (c. 465-c. 520), author of the Wenxin diaolong 文心雕龍, a book establishing rules for various literary genres, praised the Yongming style, the poetry critic Zhong Rong 鐘嶸 (c. 468- c. 518), author of the book Shipin 詩品, saw the system of Shen’s rules as fetters that impeded creativity. Based on Shen Yue’s tonal and rhyme theory, scholars of the Tang and Song 宋 (960-1279) periods developed the theory of the "eight defects of the four tone pitches" (sisheng babing 四聲八病), and it was the ground for the poetic rules (gelü 格律) of the famous Tang-period poetry.