「あいだ」and「あいだに」differ by just one「に」, but the meaning shifts subtly. While mixing them up won't break communication, this distinction is a frequent exam topic.
Core Difference
| あいだ | あいだに | |
|---|---|---|
| Following action | Continuous action | One-time / momentary event |
| Time relationship | Happening throughout the period | Happening at some point within the period |
| Keyword association | ずっと (the whole time) | 何回 (several times) / 一度 (once) |
あいだ: Doing Something the Entire Time
The following action continues throughout the entire period:
| Example | Meaning |
|---|---|
| 日本にいるあいだ、ずっと山田さんの世話になっていた。 | During my time in Japan, I was under Yamada's care the whole time. |
| 授業のあいだ、ずっと寝ていた。 | I was sleeping throughout the entire class. |
| 子どもが寝ているあいだ、本を読んでいた。 | While the child was sleeping, I was reading a book. |
Notice it often pairs with ずっと and ている to emphasize continuity.
あいだに: Something Happened During the Period
The following action is a single event that occurred at some point within the period:
| Example | Meaning |
|---|---|
| 日本にいるあいだに、何回山田さんの世話になった。 | During my time in Japan, Yamada helped me several times. |
| 授業のあいだに、3回居眠りした。 | I dozed off 3 times during class. |
| 子どもが寝ているあいだに、掃除をした。 | While the child was sleeping, I cleaned the room. |
Often pairs with specific counts, one-time completed actions, or a "while I had the chance" nuance.
Visual Comparison
あいだ (continuous):
Period ┃████████████████┃
Action ┃════════════════┃ ← happening the whole time
あいだに (one-time):
Period ┃████████████████┃
Action ┃ ★ ┃ ← happened at some point
Side-by-Side Examples
| あいだ | あいだに |
|---|---|
| 留守のあいだ、猫の世話をしていた。 | 留守のあいだに、泥棒が入った。 |
| While away, I was taking care of the cat. | While away, a burglar broke in. |
| 冬のあいだ、暖房をつけていた。 | 冬のあいだに、3回風邪を引いた。 |
| The heater was on all winter. | I caught a cold 3 times during winter. |
Summary
- あいだ = doing something continuously throughout the period (pairs with ずっと/ている)
- あいだに = something happened at a point within the period (pairs with counts / one-time actions)
- To decide: check if the following action is "ongoing" or "happened once"
Practice
1. Fill in あいだ or あいだに:
夏休みの____、毎日プールに通っていた。
Show answer
夏休みのあいだ、毎日プールに通っていた。 Going every day = continuous behavior throughout the period → あいだ.
2. Fill in あいだ or あいだに:
電車を待っている____、本を一冊読み終えた。
Show answer
電車を待っているあいだに、本を一冊読み終えた。 Finishing one book = a single completed event → あいだに.
3. How do these two sentences differ?
- a. 母が買い物に行っているあいだ、テレビを見ていた。
- b. 母が買い物に行っているあいだに、部屋を片付けた。
Show answer
- a. While Mom was shopping, I was watching TV the entire time. (continuous)
- b. While Mom was out shopping, I tidied up the room. (single completed action)