Poets should not concern themselves with theory, logic or any other convention in the use of language. Quan (筌), originally a bamboo fish-catching device, later was used as a metaphor for any form of linguistic constraint on poetic creation. The term “language trap” was first put forward by the Song Dynasty poetry theorist Yan Yu （？-1264）in his Canglang's Criticism on Poetry, a work on poetry learning and creation. It can be likened to the idea of “subtle insight.” Poetry writing has its distinct ways of thinking and aesthetic requirements. Essentially, it should express the poet's emotions and mood, and emphasize momentary feeling, rather than expound on theories or show off one's learning. Poetry learners should also avoid being shackled by theories or conventions in language use.

Poetry has its distinct subject matter and is not about book learning. It also has its distinct artistic taste and does not bother to dwell on theories. However, if poets do not read widely and pursue reason exhaustively, their poems can never reach perfection. Poetry of the highest class is not restricted by theory, logic or convention. (Yan Yu: Canglang's Criticism on Poetry)

The bamboo fish trap is used to catch fish, but the trap will be forgotten once the fish is caught. The rabbit net is used to catch rabbits, but the net will be forgotten once the rabbit is caught. Words are used to convey meaning, so we should forget the words once we have grasped the meaning. (Zhuangzi)