Japanese Chū and Jū Suffixes: During, Within and Throughout

The core idea: a pin or a highlighter

Picture a day drawn as a strip of paper. If you push a pin into it, you mark one point somewhere inside. If you run a highlighter along it, you colour the strip from end to end. Chū is the pin and jū is the highlighter.

A child asking where her father is might hear either. If he is at the office right now, the answer uses chū: at this moment he is at a point inside his work. If the speaker wants to say that work swallowed his whole day, the answer uses jū.

Chū after an activity: shigoto-chū, denwa-chū, junbi-chū

The first use to learn is a noun that names an activity plus chū. Most of these nouns are the kind that take suru: benkyō, unten, kaigi, shokuji, ryokō. The result says the activity has started and has not finished.

You will read this form before you say it, because Japanese signs are full of it. Junbi-chū on a restaurant door means not open yet. Eigyō-chū means open. Kōji-chū marks roadworks, and shiyō-chū on a lavatory door means occupied, literally in the middle of use. On the telephone, hanashi-chū means the line is engaged. In an office, chū is how you explain why you or a colleague cannot talk.

How chū and jū words are built

Both readings attach directly to a noun with nothing in between. The word that results is itself a noun, so it takes desu, no and the usual particles.

After chū, the particle changes the picture. Chū ni pins a single event inside the activity: kaigi-chū ni denwa ga narimashita, a phone rang during the meeting. Chū wa makes the whole activity the topic, often for a rule: kaigi-chū wa denwa o tsukaimasen, we don't use phones during meetings. Before a noun, use no: ryokō-chū no shashin, photos from the trip.

A period with jū takes no particle when it says how long: ichinichi-jū nemashita. A place with jū behaves like any place noun: sekai-jū de, sekai-jū no, sekai-jū o.

Jū: throughout a period or all over a place

Jū says that nothing was left out. With time it means from start to finish, and with a place it means every corner. English switches between all day, throughout the year, all over the world and the whole room, but the Japanese is the same highlighter each time. Sekai-jū is literally the whole inside of the world.

Because jū stresses completeness, it tends to carry feeling. Someone who says it rained ichinichi-jū is usually complaining. Here a friend describes a bad weekend: rain, no sleep, and lost keys.

Minimal pairs: what jū adds

In each pair below the second sentence adds jū and nothing else.

Beyond the basics: within a period, and the fixed readings

With a period of time and ni, the pin gives a deadline: the action happens once, somewhere before the period ends. Konshū-chū ni henji o kudasai asks for a reply by the end of this week. This is the pattern for promises, requests and delivery windows.

Here the core idea meets its limit. By meaning, every within word ought to be read chū, yet a handful are read jū: kyō-jū ni, ashita-jū ni, kotoshi-jū ni. The pin and the highlighter do not explain these, and it is more honest to call them habits of the language. Gozen-chū goes the other way: it is always chū, even when you mean the whole morning.

Beyond the basics: how to predict the reading

When you meet a new word with this suffix, look at the noun in front and ask three questions in order.

• Is it an activity, such as a meeting, a trip or a repair? Read chū
• Is it a place or a body, such as a town, a house or a country? Read jū
• Is it a period with no ni, meaning the whole of it? Read jū
• Is it a period with ni, meaning within? Read chū, except for kyō, ashita and kotoshi

There is a loose pattern behind the exceptions. Kyō, ashita and kotoshi are native Japanese words, and they take jū. Konshū, kongetsu and gozen are compounds borrowed from Chinese, and they take chū. It is a tendency rather than a law, since ichinichi and sekai are also Chinese-style compounds and take jū, but it helps the fixed words stick.

Neighbours: aida, saichū and naka

Aida and aida ni do the same two jobs as the highlighter and the pin, but they follow verbs and clauses as well as nouns. Use chū when a compact activity noun exists, and aida when you need a verb: Nihon ni iru aida. Saichū is a sharper pin. It means at the very height of something and nearly always introduces an interruption.

Naka is the same kanji used as an independent word for physical or abstract insides. It needs no before it, kaban no naka, whereas the suffix attaches directly.

Common mistakes with chū and jū

The first mistake is reading every case as chū. Ichinichi-chū and sekai-chū are wrong. Learners meet chū first, in words like benkyō-chū, and carry it over. Whole periods and places take jū: ichinichi-jū, sekai-jū.

The second is kyō-chū ni, which is wrong for the opposite reason: the learner has understood the rule and applied it where habit overrides it. Say kyō-jū ni.

The third is attaching chū to a verb. Tabete iru chū is wrong. It copies English while eating, but chū needs a noun. Say shokuji-chū, or tabete iru aida.

The fourth is adding ni to a throughout expression. Ichinichi-jū ni nete imashita is wrong, because ni turns a span into a deadline. Durations take no particle: ichinichi-jū nete imashita.

The fifth is using chū for a lasting state. Kekkon-chū is wrong for I am married. Chū suggests a phase with an end in sight, which is why ryūgaku-chū and nyūin-chū work. For marriage, say kekkon shite imasu.