間 describes an interval, 間に places something within that interval, and うちに can mean while a condition still holds. 読んでいる間 presents reading as lasting through a period; 読んでいる間に can place an event or completed task within it. 熱いうちに食べる urges action while food is hot, while 話しているうちに can describe a gradual change.
also written aida / aidani / uchini / 〜ている間に / 〜ないうちに
間 — throughout a period · 間に — within a period · うちに — before a state changes; as something continues
Sentences
6 sentences, word by word
間 · the whole stretch
polite
、。
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子供
こども ［0］
child
noun · the subject of the sleeping, marked が inside the clause
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が
が
marks the subject
particle · what the sentence is about — with 好き, 分かる and potentials, the object
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寝ている
ねている
is sleeping
ている form of 寝る · describes the ongoing sleeping state
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間
あいだ ［0］
during the whole time
noun · no に, so the second event fills the entire period
間N3throughout
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本
ほん ［1］
book
noun · the object of the reading
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を
を
marks the direct object
particle · pronounced お
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読んでいました
よんでいました
was reading
past ている of 読む · a lasting action, matching the lasting period
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I read a book the whole time the child was asleep.
間に · one moment inside
polite
、。
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子供
こども ［0］
child
noun · the same sleeping child; this example places a ringing event within that period
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が
が
marks the subject
particle · what the sentence is about — with 好き, 分かる and potentials, the object
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寝ている
ねている
is sleeping
ている form of 寝る · the period inside which something happened
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間
あいだ ［0］
while
noun · followed by に to place the event within the period
間にN3within a period
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に
に
to; at; into
particle · a point something reaches — a place, a time, a person, or a state
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電話
でんわ ［0］
phone
noun · the subject of the ringing
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が
が
marks the subject
particle · what the sentence is about — with 好き, 分かる and potentials, the object
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鳴りました
なりました
rang
polite past of 鳴る · a one-off event, which is why に is needed
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The phone rang while the child was asleep.
うちに · while it lasts
polite
。
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熱い
あつい ［2］
hot
い-adjective · hot to the touch, unlike 暑い for weather
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うちに
うちに
while it still is
expression · the state is fading, so the moment should be used
うちにN3while it still lasts
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食べて
たべて
eat
て-form of 食べる · a request once ください follows
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ください
ください
please (do)
polite request · from くださる
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Please eat it while it's still hot.
ないうちに · before it happens
polite
。
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忘れない
わすれない
not forget
negative of 忘れる · the state that has not yet ended
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うちに
うちに
before
expression · while the not-forgetting still holds, which means 'before'
ないうちにN3before it happens
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メモ
メモ
a note
noun · loanword, used as a noun and with する as a verb
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します
します
will make
polite of する · turning メモ into an action
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I'll write it down before I forget.
間に · while someone is out
polite
、。
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母
はは ［1］
my mother
noun · your own mother, spoken to someone outside the family
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が
が
marks the subject
particle · what the sentence is about — with 好き, 分かる and potentials, the object
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留守
るす ［1］
out; away from home
noun · being absent from home, so の links it to 間
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の
の
linking the state to the period
particle · connects 留守 to 間
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間
あいだ ［0］
while
noun · with に, the cleaning is completed within the absence
間にN3within a period
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に
に
to; at; into
particle · a point something reaches — a place, a time, a person, or a state
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掃除
そうじ ［0］
cleaning
noun · made into a verb by する
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を
を
marks the direct object
particle · pronounced お
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しました
しました
did
polite past of する · the completed action within the period
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I did the cleaning while my mother was out.
うちに · while you still can
plain
。
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若い
わかい ［2］
young
い-adjective · a temporary state; here, the advice concerns using that opportunity
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うちに
うちに
while you still are
expression · the window closes, so the advice is to act now
うちにN3while it still lasts
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旅行
りょこう ［0］
travel
noun · made into a verb by する
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を
を
marks the direct object
particle · pronounced お
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した
した
do
plain past of する · the た-form used here to give advice
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ほうがいい
ほうがいい
you'd better
expression · Vたほうがいい is a common pattern for positive advice
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You should travel while you're young.
Structure
How each one attaches
寝ている / 留守の＋間
寝ている間. No に, and the second verb describes something that lasted the whole time.
寝ている / 留守の＋間に
寝ている間に. An event occurs or an action is completed within the period.
V dictionary / Vている / Vない / い-adj / な-adj な / N の＋うちに
熱いうちに, 元気なうちに, 学生のうちに. The meaning depends on the main clause.
忘れ / 冷め / 降ら＋ないうちに
忘れないうちに. Before it happens — the negative shape is extremely common and worth learning as a unit.
Meaning
間 vs 間に vs うちに
間 focuses on duration; 間に places something within it. 子供が寝ている間、本を読んでいました presents reading as continuing during the sleep. With 間に, the ringing happens within that period. The event need not be instantaneous: cleaning can also be completed within someone’s absence.
うちに can emphasize an opportunity before a change. 熱いうちに食べてください means to eat while the food is still hot. This does not require the change to be imminent.
うちに also describes a change during an ongoing action or state. For example, 話しているうちに緊張が消えた means the nervousness disappeared as the conversation continued. This use does not tell anyone to hurry.
ないうちに often means “before”. 忘れないうちにメモします means “I’ll write it down before I forget.” Other contexts describe a change during a negative state, as in しばらく会わないうちに, “during the time we did not see each other.”
Watch out
Where these three go wrong
Treating 間に as an instant only
間に can contain an event or an activity completed within the period. The cleaning example takes time; に does not make it instantaneous.
Treating every changing state as incompatible with 間に
うちに is natural when you want to emphasize doing something before a state changes. 間に can also describe a period during which a state holds. The difference is viewpoint, not a blanket ban on changing states.
Reading ないうちに as a negative command
忘れないうちに describes the time before forgetting. It does not negate the main action メモします.
Forgetting の after a noun
Use 留守の間に, with の linking the noun to 間. With うちに, nouns also take の and な-adjectives take な: 学生のうちに, 元気なうちに.
Also asked
Questions people ask about 間, 間に and うちに
What does に change?
間 describes an action or state extending through a period. 間に places an event or its completion inside that period; it need not occupy just one instant.
Why choose 熱いうちに?
It emphasizes eating before the food cools. Choose うちに for that opportunity-before-change meaning, rather than treating 間に as universally ungrammatical with a changing state.
Is ないうちに the same as 前に?
In 忘れないうちに, both can express “before.” うちに highlights the state that still holds. It also has other uses, including changes that occur while an action or state continues.
Can うちに attach to a verb?
Yes. Dictionary forms, ている forms and negative forms occur: 日本にいるうちに, 話しているうちに, 雨が降らないうちに. It also follows い-adjectives, な-adjective + な, and noun + の.
References
Sources and usage notes
Japan Foundation: 表現意図 — とき (2) — Contrasts duration with completion within a period and the opportunity-before-change meaning of うちに.
Japan Foundation: うちに / ないうちに — Lists attachment patterns and both opportunity-before-change and change-during-an-action uses.
Japan Foundation: Vたほうがいいです — Explains the positive-advice pattern used in the travel example; notes that dictionary-form ほうがいい also exists with a different use.
