Four-character idioms, or chéng yǔ (成語, literally "to become (part of) the language") are widely used in 文言 wényán. Wényán refers to literary and artificial classical ways of expression used in the Chinese written language from Antiquity to until 1919. Wényán can be compared to the way Latin was used in the Western world in science until recently.

Chéng yǔ are mostly derived from ancient literature. The meaning of a chéng yǔ usually surpasses the sum of the meanings carried by the four characters, as chéng yǔs are often intimately linked with the myth, story or historical fact from which they were derived. As such, chéng yǔ do not follow the usual grammatical structure and syntax of the modern Chinese spoken language, and are instead highly compact and synthetic.

Chéng yǔ in isolation are often unintelligible to modern Chinese, and when students in China learn chéng yǔ in school as part of the wényán curriculum, they also need to study the context from which the Chéng yǔ was born. Often the four characters reflect the moral behind the story rather than the story itself. For example, the phrase "破釜沉舟" (pò fǔ chén zhōu) literally means "crack the woks and sink the boats." It was based on a historical account where General Xiang Yu ordered his troop to destroy all cooking utensils and boats after crossing a river into the enemy's territory. He won the battle because of this "no-retreat" policy. The phrase is used when one succeeds by burning the bridge. This particular idiom cannot be used in a losing scenario because the story behind it does not describe a failure.

Another example is 瓜田李下 (guātián lǐxià) which literally means melon field, under the plums. It is an idiom that has a deeper meaning that implies suspicious situations. It is derived from an excerpt from a poem (樂府詩《君子行》) from the Han dynasty. The poem contains two phrases 瓜田不納履，李下不整冠 which describe a code of conduct that says "Don't adjust your shoes in a melon field and don't tidy your hat under the plum trees" in order to avoid suspicion of stealing. The literal meaning of the idiom is impossible to understand without the background knowledge of the origin of the phrase.

However, that is not to say that all chengyu's are born of an oft-told fable; indeed, chengyu's which are free of metaphorical nuances pervade amidst the otherwise contextually-driven aspect of vernacular Chinese. An example of this is 言而无信 (yán ér wú xìn, literally "speaks yet (is) without trust), which refers to an individual who cannot be trusted despite what he says, or essentially a deceitful person. The idiom itself is not derived from a specific occurrence from which a moral may be explicitly drawn; instead, it is succinct in its original meaning and would likely be intelligible to an individual learned in formal written Chinese. Note that the only classical-vernacular discrepancy present in this chengyu lies in the fact that 言 is no longer used as a verb in modern Chinese.

The following three examples show that the meaning of the idiom can be totally different by only changing one character.

• 一日千秋 (yī rì qiān qiū)
  • Literal: One day, a thousand autumns.
  • Usage/Moral: implies rapid changes; one day equals a thousand years

• 一日千里 (yī rì qiān lǐ)
  • Literal: One day, a thousand miles.
  • Usage/Moral: implies rapid progress; traveling a thousand miles in a day

• 一日三秋 (yī rì sān qiū)
  • Literal: One day, three autumns.
  • Usage/Moral: greatly missing someone; one day feels as long as three years

In Japanese, four-character idiom (四字 yoji four Chinese characters + 熟語 jukugo idiom) is a common technique to make a memorizable phrase or idiom. The term 四字熟語 itself is a four-character idiom. The term is also sometimes referred as 四字成句 (yoji + seiku idiom). Many idioms were adopted from Chinese writings and many idioms have same meaning as in Chinese. Among idioms are:

• 傍若無人 (bō jaku bu jin)
  • Literal: As if there is nobody beside (you).
  • Usage/Moral: One has a very high and often misguided opinion of self and acts any way s/he wants that tend to cause trouble for others. It is rarely used positively.
  • Source: The Biography of Xiè Shàng (謝尚), Volume 79, the Chronicle of Jìn.

• 起承転結 (ki shō ten ketsu)
  • Literal: Start, Continue, Change, Conclusion
  • Usage/Moral: This is the simplest way to make a story or a poem.
  • Source:

See also: Japanese language, Idiom, Wikiquote:Japanese proverbs, Wikiquote:Chinese proverbs, Chinese characters