In the Sinosphere, the word , realized in Japanese and Korean as ' and in Standard Chinese as , meaning 'to lack' or 'without', is a key term in the vocabulary of various East Asian philosophical and religious traditions, such as Buddhism and Taoism.
The Old Chinese * () is cognate with the Proto-Tibeto-Burman *, meaning 'not'. This reconstructed root is widely represented in Tibeto-Burman languages; for instance, means 'not' in both Tibetan and Burmese.
The Standard Chinese pronunciation of (; 'not', 'nothing') historically derives from the Middle Chinese , the Late Han Chinese muÃÂ, and the reconstructed Old Chinese *.
Other varieties of Chinese have differing pronunciations of . Compare Cantonese ; and Southern Min (Quanzhou) and (Zhangzhou).
The common Chinese word () was adopted in the Sino-Japanese, Sino-Korean, and Sino-Vietnamese vocabularies. The Japanese kanji has readings of or , and a (Japanese reading) of . It is a fourth-grade kanji. The Korean is read (in Revised, McCuneâÂÂReischauer, and Yale romanization systems). The Vietnamese Hán-Viá»Ât pronunciation is or .
Some English translation equivalents of or are:
In modern Chinese, Japanese and Korean it is commonly used in combination words as a negative prefix to indicate the absence of something (no ..., without ..., un- prefix), e.g., // () for "wireless". In Classical Chinese, it is an impersonal existential verb meaning "not have".
The same character is also used in Classical Chinese as a prohibitive particle, though in this case it is more properly written .
In traditional Chinese character classification, the uncommon class of phonetic loan characters involved borrowing the character for one word to write another near-homophone. For instance, the character originally depicted a winnowing basket (), and scribes used it as a graphic loan for (, "his; her; its"), which resulted in a new character () (clarified with the bamboo radical ) to specify the basket.
The character () originally meant "dance" and was later used as a graphic loan for , "not". The earliest graphs for pictured a person with outstretched arms holding something (possibly sleeves, tassels, ornaments) and represented the word "dance; dancer". After meaning "dance" was borrowed as a loan for meaning "not; without", the original meaning was elucidated with the radical , "opposite feet" at the bottom of , "dance".
The Gateless Gate, a 13th-century collection of Zen kà Âan, uses the word wu or mu in its title (Wumenguan or Mumonkan ç¡éÂÂéÂÂ) and first kà Âan case ("Zhao Zhou's Dog" è¶Âå·ÂçÂÂÃ¥ÂÂ). Chinese Chan calls the word mu ç¡ "the gate to enlightenment". The Japanese Rinzai school classifies the Mu Kà Âan as hosshin "resolve to attain enlightenment", that is, appropriate for beginners seeking kenshà  "to see the Buddha-nature".
Case 1 of The Gateless Gate reads as follows:
The koan originally comes from the Zhaozhou Zhenji Chanshi Yulu (), The Recorded Sayings of Zen Master Zhao Zhou, koan 132:
The Book of Serenity (), also known as the Book of Equanimity or more formally the Hóngzhì Chánshë GuÃÂnglù (), has a longer version of this koan, which adds the following to the start of the version given in the Zhaozhou Zhenji Chanshi Yulu.
In the original text, the question is used as a conventional beginning to a question-and-answer exchange (mondo). The reference is to the MahÃÂyÃÂna MahÃÂparinirvÃÂá¹Âa Sà «tra which says for example:
Koan 363 in the Zhaozhou Zhenji Chanshi Yulu shares the same beginning question.
This koan is one of several traditionally used by Rinzai school to initiate students into Zen study, and interpretations of it vary widely. Hakuun Yasutani of the Sanbo Kyodan maintained that:
This koan is discussed in Part 1 of Hau Hoo's The Sound of the One Hand: 281 Zen Koans with Answers. In it, the answer of "negative", mu, is clarified as although all beings have potential Buddha-nature, beings who do not have the capacity to see it and develop it essentially do not have it. The purpose of this primary koan to a student is to free the mind from analytic thinking and into intuitive knowing. A student who understands the nature of his question would understand the importance of awareness of potential to begin developing it.
The Japanese scholar made the following comment on the two versions of the koan:
A similar critique has been given by Steven Heine:
In Robert M. Pirsig's 1974 novel Zen and the Art of Motorcycle Maintenance, mu is translated as "no thing", saying that it meant "unask the question". He offered the example of a computer circuit using the binary numeral system, in effect using mu to represent high impedance:
The word features prominently with a similar meaning in Douglas Hofstadter's 1979 book, Gödel, Escher, Bach. It is used fancifully in discussions of symbolic logic, particularly Gödel's incompleteness theorems, to indicate a question whose "answer" is to either un-ask the question, indicate the question is fundamentally flawed, or reject the premise that a dualistic answer can be given.
"Mu" may be used similarly to "" or "not applicable," a term often used to indicate that the question cannot be answered because the conditions of the question do not match the reality. An example of this concept could be with the loaded question "Have you stopped beating your wife?", where "mu" would be considered the only respectable response.
The programming language Raku uses "Mu" for the root of its type hierarchy.