语言学条件的成立与语体的雅化是古典诗歌特定诗体流行的前提与助援。“四字句”的成立是七言成体的语言学前提，也是依赖“二二”节奏的四言诗最终衰落的要因。而应制对于七言的语体提升则是七言迅速发展的重要推动。七言近体之所以能够与五言近体并立，自语法层面而言，七言能够强化殊相，利于拓展写景、言情、论理的表现空间，且更具语法密度；于韵律层面，七言“上四下三”结构所形成的表现功能，则较五言更具修饰性，情感表现的层次与空间亦更为丰富。

Linguistic conditions and the refinement of language style are the prerequisite and facilitator for the popularity of specific poetry styles in Chinese classical poetry. The formation of four-character sentence was the linguistic prerequisite for seven-character poetry, and was also the fundamental reason for the decline of four-character poetry relying on “two-two” rhythm. The improvement of seven-character style resulted from imperial order was an important impetus for the rapid development of seven-character poetry. The grammatical reason behind the parallel between seven-character poetry and five-character poetry highlighted their difference, making seven-character lines more suitable to write about scenery, emotion and argument because of its representation space and grammatical density.  In terms of prosody, the “four-three” structure of seven-character line formed an expressive feeling that was more decorative and explicit than five-character sentence.