情发于声
当人们受到外界事物的触发，情感在心里激荡，就会用诗歌表现这种情感并用一定的音乐旋律咏唱出来。见于《毛诗序》。这是中国古代关于诗歌起源的一种说法，与《尚书》中的“诗言志”大体接近且一脉相承。在上古时代，诗歌、音乐、舞蹈三位一体，密不可分，“情发于声”体现了上古诗歌的主要特点。后来诗歌逐渐成为单纯的语言艺术，与音乐、舞蹈脱节，“情发于声”的说法退出历史舞台。
Feelings Find Expression in Musical Poetry
When feelings surge up in people's hearts due to inspiration from external objects, they will find expression in poetry and music. This is stated in "Introductions to Mao's Version of The Book of Songs," echoing the idea that "poetry expresses aspirations" documented in The Book of History. In pre-Qin China, poetry, music and dance were all closely linked together, even merged into one. This idea reflected the special features of that era. Later, poetry became an independent art of language, divorced from music and dance. Thus, the idea took leave from the literary scene.
引例
大凡人之感于事，则必动于情，然后兴于嗟叹，发于吟咏，而形于歌诗矣。（白居易《策林·六十九·采诗以补察时政》）（一般来说，人们被外界事物感动，就必然激发内心的情感，随之而发出嗟叹的声音，用音乐将这种感情吟唱出来，就产生了可以歌唱的诗。）
