Poetry have challenged the traditional definitions of the sonnet form, rendering entire sequences of "sonnets" that often lack rhyme, a clear logical progression, or even a consistent count of fourteen lines. "Shi" () Is the main type of Classical Chinese poetry. Within this form of poetry the most important variations are "folk song" styled verse ("yuefu"), "old style" verse ("gushi"), "modern style" verse ("jintishi"). In all cases, rhyming is obligatory. The Yuefu is a folk ballad or a poem written in the folk ballad style, and the number of lines and the length of the lines could be irregular. For the
Sonnet 151 steer his actions. It uses the body as a metaphor for the penis, "rising" and "falling" with an erection when aroused, and so reduces the speaker to nothing more than his phallus; by giving in to his desires he enslaves himself to the "Dark Lady". Sonnet 151, with a "bawdy chronicle of erection and detumescence," contrasts with Sonnet 55's "grandiloquent expression," but their theme is the same: "what changes, what remains." Sonnet 55 "celebrates ... love and poetry that endure[s]" where Sonnet 151 "contemplates the inevitability of change..." Sonnet 151 has been compared to a verse by 17th-century author Joseph