a story, dialogue, question, or statement which is used in Zen practice to provoke the "great doubt" and to practice or test a student's progress in Zen.
Koan practice developed from a literary practice, styling snippets of encounter-dialogue into well-edited stories. It arose in interaction with "educated literati". There were dangers involved in such a literary approach, such as ascribing specific meanings to the cases. Dahui Zonggao is even said to have burned the woodblocks of the Blue Cliff Record, for the hindrance it had become to study of Chán by his students. Kōan literature was also influenced by the pre-Zen Chinese tradition of the "literary game"—a competition involving improvised poetry.
The style of writing of Zen texts has been influenced by "a variety of east Asian literary games":
The extensive use of allusions, which create a feeling of disconnection with the main theme;
Indirect references, such as titling a poem with one topic and composing a verse that seems on the surface to be totally unrelated;
Inventive wordplay based on the fact that Hanzi (Chinese characters) are homophonic and convey multiple, often complementary or contradictory meanings;
Linking the verses in a sustained string based on hidden points of connection or continuity, such as seasonal imagery or references to myths and legends.
