Four is not a particularly lucky number in Japanese. Having one reading in common with the word for “death,” it tends to be avoided in everyday situations from annual company health checks (no locker No. 4 when you change clothes, as this might forebode a bad test result) to wedding ceremonies (never give ¥40,000 if you want the marriage to last).

Yet there is one phenomenon where four doesn’t seem to have any negative implications at all: yoji jukugo (四字熟語). These are “four-character idioms,” as the term literally translates, with a distinctive, often proverbial or aphoristic, meaning. While many of these constructions are somewhat quaint and reserved for special situations, they also occur in large quantities in everyday language.

I recently conducted a little survey, in which I asked about 60 of my students to each list three representative yoji jukugo. The most frequent term, given by 38 percent, was isseki nichō (一石二鳥), a most faithful rendition of the English “kill two birds with one stone.” Next was ichigo ichie (一期一会), a reminder to “treasure every encounter, for it will never recur.” Originally an expression from tea ceremony, the popularity of this saying is evidenced by the fact that the Japanese Wikipedia page offers 11 disambiguation options, including the domestic subtitle of the 1994 box office hit “Forrest Gump.”

Third came jakuniku kyōshoku (弱肉強食), the Japanese equivalent of “the law of the jungle.” Sixteen percent went for this “weak meat, strong eat” slogan, as it translates verbatim. Another two students gave a slightly more urban version, yakiniku teishoku (焼肉定食, set meal with grilled meat), which has the same second and fourth characters and a very similar sound structure. And though the two students can’t have been too serious about this —it was an anonymous survey, so there was no way to ask them — they did have a point.

After all, far from being the exclusive property of the realm of poems and proverbs, strings of four characters are a quite frequent sight in more mundane contexts, too. In commercial language, for instance, many messages take the form of a yoji jukugo. Just walk along an ordinary shopping street and you will be hard-pressed not to notice kayō teikyū (火曜定休, closed on Tuesdays), nenjū mukyū (年中無休, open all year round), honjitsu gentei (本日限定, only today), zenpin hangaku (全品半額, everything half price), ōmori muryō (大盛無料, big serving free of charge), or even gakuwari datsumō (学割脱毛, student-discount depilation).

A second favorable domain for four-character expressions is in public orders and warnings. Like in the commercial sphere, they come in very handy here because they can condense a high amount of information into a maximally short form. Take, for instance, the term shūjitsu kin’en (終日禁煙), which declares not only that smoking is prohibited, but also that this prohibition applies all day long — and all that in four characters.

Speaking of prohibitions, a vast number of four-letter expressions in the public domain contain the term kinshi (禁止, prohibition). They include tachiiri kinshi (立入禁止) and shinnyū kinshi (進入禁止), both of which prohibit trespassing; chūsha kinshi (駐車禁止) and chūrin kinshi (駐輪禁止) to prevent parking offenses by cars or bicycles, respectively; as well as usetsu kinshi (右折禁止) and sasetsu kinshi (左折禁止), which forbid right or left turns. Particularly hazardous acts are prohibited with genkin (厳禁, strictly forbidden), as in kaki genkin (火気厳禁, “No open flames”) and dosoku genkin (土足厳禁, “Remove your shoes before entering”).

Another common component of four-character warnings is chūi (注意, attention). Indispensable for drivers, it can be deployed to announce all manner of potential dangers ahead, including rear-end collisions (tsuitotsu chūi, 追突注意), the merging of two lanes (gōryū chūi, 合流注意), and children suddenly rushing across the road (tobidashi chūi, 飛(び)出(し)注意). Depending on what part of the country you are in, you may also come across warnings about animals crossing (dōbutsu chūi, 動物注意), frozen road surfaces (tōketsu chūi, 凍結注意), strong winds (kyōfū chūi, 強風注意), falling rocks (rakuseki chūi, 落石注意) and avalanches (nadare chūi, 雪崩注意).

But you don’t have to go that far. Even the average public men’s room is equipped with a couple of four-character expressions. Apart from shiyō kinshi (使用禁止, usage forbidden) and shiyō chūshi (使用中止, usage interrupted), both of which designate presently unusable devices, my favorite is ippo zenshin (一歩前進). This is a little reminder to “progress one more step” towards the porcelain in order to help keep the toilet floor clean.

To be sure, not every four-character expression is a yoji jukugo. Yet while it may be more erudite to declare your intention to “kill two birds with one stone” than “watch out for wild boars on the road,” saying it in four characters seems to be a pervasive stylistic device permeating all areas of life, from the pedestrian to the profound.