The word 間 (あいだ) can be used to create sentences that mean “While Action A, Action B.” But did you know that the meaning changes in an important way depending on whether you use に after the word 間?

This grammar point came up in a discussion within Satori Reader, a Japanese language learning app. Since 間 is such an important grammar point, we wanted to clarify the difference to help you more accurately comprehend what you read in Japanese.

間 vs 間に

The word 間 can be used to make phrases that mean “While Action A, Action B.” For example:

私が仕事をしている間、彼は寝ていた。
While I was working, he was sleeping.

Sometimes you might see the word 間 with に after it, while sometimes it simply stands alone, as above. This might lead you to wonder whether it makes a difference whether you use に. It does. (This explanation is based on the one given by Makino and Tsutsui in A Dictionary of Basic Japanese Grammar, page 70.)

Without に, Action A and Action B are understood to cover the same span of time. For example:

私が仕事をしている間、彼は本を読んでいた。
While I was working, he was reading a book.

On a timeline, the two actions look like this:

With に, Action B takes place sometime within the span of Action A, but not necessarily for the entire span. For example:

私が仕事をしている間に、彼は昼ごはんを食べた。
While I was working, he ate lunch.

For this sentence, the timeline looks like this:

We don’t know exactly how long the eating of lunch took, only that it happened sometime within the span of the first person working.

Because of this fact, if Action B is an instantaneously completing action, like “to wake up,” you actually must use the に. The reason is that it doesn’t make sense to speak of “waking up” over some extended period of time. You’re sleeping until, in an instant, you wake up.

私が仕事をしている間に、彼は目を覚ました。
While I was working, he woke up.

Conclusion

Hopefully this helped you get a better understanding of 間 and 間に.

This kind of discussion is happening every day on Satori Reader, so if you enjoyed this, you’ll find lots more like this there.