We have two basic ways of expressing simultaneous actions in Japanese, e.g. “I ate dinner while watching television”. Both translate as “while” in English, but the usage in Japanese is different.
～ながら
Here is the basic structure for this grammar:
【Verb: Stem】ながら【Verb】
テレビを見ながら晩ご飯を食べる。
Eat dinner while watching television.
仕事のことを考えながら寝る。
To go to sleep thinking about work.
働きながら大学を卒業する。
To work your way through university.
What about the order? Well, grammatically it doesn’t matter but the final verb can be considered to be the “main” action.
テレビを見ながら晩ご飯を食べる。
To eat dinner while watching television.
晩ご飯を食べながらテレビを見る。
To watch television while eating dinner.
～ている間に
【Verb: Present Participle】間に
The kanji 間 we’ve seen used as a counter for time periods.
１時間。
One hour.
３週間。
Three weeks.
In this structure 間 is a noun which the present participle is modifying to express the time period while doing something.
妊娠している間にお酒を控える。
To refrain from drinking while pregnant.
The critical difference between ながら and ～ている間に is that in the case of the former both actions will be performed by the speaker. On the other hand, ～ている間に is typically used when something else happens that is outside of your control while you are doing something.
昨日、寝ている間に泥棒が部屋に忍び込んで財布を盗んだ。
Yesterday while I was sleeping a burglar crept into my room and stole my wallet.
テレビを見ている間に友達から電話がかかってきました。
To get a phone call from a friend while watching television.
A Critical Distinction: 間に vs. 間
It is very important to understand the role of the particle に here. When you use 間に (with “ni”), it means the second action was a momentary event that happened at some point within that time frame. If you remove “ni” and just use 間, it means the second action was continuous and lasted for the entire duration of the first action.
私が買い物をしている間に、彼はカフェでコーヒーを飲んだ。
While I was shopping, he drank a coffee at the cafe. (A single, completed action during the timeframe).
私が買い物をしている間、彼はずっとカフェで待っていた。
While I was shopping, he waited at the cafe the whole time. (A continuous action parallel to the timeframe).
Using Nouns and Adjectives
Because 間 is a noun, it does not only connect to verbs. You will frequently see it attached to other nouns using the particle の, or to adjectives using standard grammar rules.
夏休みの間に、運転免許を取りました。
During the summer holidays, I got my driver’s license.
留守の間に、荷物が届いた。
While I was not at home, a package arrived.
独身の間に、いろいろな国へ旅行したい。
While I am single, I want to travel to various countries.