Beiqu (北曲), the Northern Opera, originated in northern China. It was based on northern folk songs that were popular in the Northern Song Dynasty or earlier, and its lyrics were often funny and simple. After the Southern Song Dynasty, northern China fell under the rule of the Jin and Yuan dynasties. As a result, songs, dances, and musical elements of Nüzhen, Mongolian and other ethnic groups were widely incorporated into the Northern Opera, making it a unique form of opera. At the same time, many writers became interested in the Northern Opera and wrote large numbers of excellent opera works. Compared with the lyrics of the literati of the Song period, the Northern Opera was simple, direct and sincere, and there was greater freedom in arranging rhythm. The Northern Opera was performed mainly in the form of short lyrics and cycles. As they dealt with various social themes, operas performed in this artistic form were referred to as zaju (杂剧opera of various themes). Writers in the Yuan Dynasty had low social status, so they wrote a large number of Northern Opera works to express their emotions and views. They are represented by Guan Hanqing, Ma Zhiyuan, Bai Pu and Zheng Guangzu, collectively known as the top four Yuan Opera writers.
Song Dynasty poetry and the Southern and Northern operas that were popular from the Jin and Yuan dynasties onwards were not music from ancient times, but they were still divided into Do, Re, Mi, Sol and La. Some people could produce these kinds of music, and the audience could also tell if it had the right rhyme. Actually, what was done was to restore ancient music based on current music and make popular music more refined… Rhymes were evaluated through singing, the sound of musical instruments was then determined according to standard rhymes, and this made it possible to restore the music of the Xia, Shang, and Zhou dynasties. (Qiu Jun: Supplement to the Exposition on the Great Learning)
Only two people sang in the performance. One was the male character and the other was the female character. When others joined in, they only talked. As they did not sing, they were known as supporting speakers. Singing was done by leading performers, and speakers only played a supporting role. By the time of the late Yuan and early Ming dynasties, however, this practice changed due to the influence of the Southern Opera, and all performers sang and they were no longer classified as leading or supporting roles. (Mao Qiling: Mao Qiling’s Remarks on Poetry)