diangu 典故, literary allusion

The expressions diangu 典故 or zhanggu 掌故 are used for references in poetry or prose works to ancient stories or words with historical origins and sources.

Scholars of Chinese linguistics and comparative literature discern two main types: Shidian 事典 (historical allusions) and yudian 語典 (linguistic allusions). The term shidian refers to allusions from historical or legendary stories with traceable sources. The expressions of these allusions (also known as diangu biaoti 典故標題, diangu biaomu 典故標目, diangu timudiangu timing 典故題名 or diangu mingmu 典故名目) are condensed expressions derived from the original stories, using representative keywords. These expressions function similarly to linguistic words and phrases but are more structurally flexible and do not have a fixed lexical form. Instead, they follow the author's intent and stylistic choices.

Another common way allusions are formed is by summarising their linguistic structures when used in poetry or prose. Allusions derived directly from their sources tend to be straightforward, while those shaped through literary usage vary widely, as different authors employ them in diverse ways. As a result, a single allusion may have multiple forms, a phenomenon known as "one allusion, multiple expressions" (yi dian duo cheng 一典多稱).

For example, the story of Che Yin 車胤, a Jin-period 晉 (265-420) scholar who was too poor to afford lamp oil and collected fireflies in a silk pouch to use their glow for nighttime reading, has been condensed into various allusion names. These include nang ying zhao du 囊螢照讀 "reading by fireflies in a pouch", shou ying 收螢 "gathering fireflies", ji ying 集螢 "collecting fireflies", ju ying 聚螢 "accumulating fireflies", dushu ying 讀書螢 "fireflies for reading", ying an 螢案 "firefly-lit desk", ying xi 螢席 "firefly-lit mat", Shaan ying 陝螢 "fireflies from Shaanxi", Wuzi chuang 武子窗 "Wuzi's window", and Che Yin nang ying 車胤囊螢 "Che Yin's firefly pouch" — among many others.

As for yudian (linguistic allusions), they refer to ancient vocabulary with traceable origins that differ from general words and phrases. Structurally, yudian are not as complex and variable as shidian. In terms of content, yudian are not based on complete stories; rather, they only retain the literal and extended meanings of the allusion itself. Therefore, compared to shidian, yudian have a narrower and more straightforward connotation. They often carry both literal and extended meanings.

The phrase yi yin tou yu 以蚓投魚 "use an earthworm to bait a fish", for instance, is a literary allusion meaning "to discard something insignificant and gain something valuable." It comes from the biography of Xue Daoheng 薛道衡 (540-609; ch. 57) in the official dynastic history Suishu 隋書: The envoy of Chen 陳 (557-589), Fu Chuo 傅綽, was sent on a diplomatic mission to (Northern) Qi 北齊 (550-577), where Xue Daoheng, serving as Director of Receptions (zhukelang 主客郎), was responsible for receiving him. Fu Chuo composed a fifty-rhymes poem as a gift, and Xue Daoheng responded with one in return, which was highly praised in both the northern and southern regions. The historian Wei Shou 魏收 (507-572) commented: "This is what Fu Zai meant by using an earthworm to bait a fish." From this concrete situation, the words "use an earthworm to bait a fish" became a linguistic allusion used to describe situations where a minor sacrifice leads to a significant gain. It appears, for instance, in the Youxue qionglin 幼學瓊林, a book with moral instructions for young learners, with the words, "Releasing an owl while imprisoning a phoenix (fang xiao qin feng 放梟囚鳳) is cruel and misguided; using an earthworm to catch a fish is simply the natural order — losing something small to gain something big."

Literary allusions are so widespread in Chinese literature that specialised dictionaries explain them. Diangu often consists of but two or four words and can sometimes only be recognised by erudite readers.

The word diangu can also be used with the same meaning as gushi 故事, with the judicial meaning of "established precedent" (chengli 成例).