Yuka同時に and 一斉に can both mean “at the same time” — but they’re used in different situations. Let’s compare!
| Word | Reading | Core Meaning |
|---|---|---|
| 同時に | doujini | at the same time (two or more things happening simultaneously) |
| 一斉に | isseini | all at once (a group doing something simultaneously) |
同時に: Simultaneously
同時に (doujini) describes two or more things happening at the same time — parallel events or actions:
- 二つのことを同時にするのは難しい。 — It’s hard to do two things at the same time.
- 彼らは同時に同じことを言った。 — They said the same thing at the same time.
- 音楽を聴きながら同時に勉強できる。 — I can study while listening to music simultaneously.
一斉に: All at Once (Group)
一斉に (isseini) emphasizes a group doing something together, simultaneously. There’s a sense of coordination or unified action:
- 生徒たちが一斉に立ち上がった。 — The students all stood up at once.
- 花火が一斉に打ち上げられた。 — The fireworks were launched all at once.
- 一斉に拍手が起きた。 — Applause broke out all at once.
ReiCan I use 同時に for a group doing something together?
YukaYou can, but 一斉に is more natural for groups — it has that “in unison” feeling. 同時に is better for two events happening in parallel.
Comparison Table
| Feature | 同時に | 一斉に |
|---|---|---|
| Focus | Two parallel events | Group acting in unison |
| Group action | Possible | Primary use |
| Formality | Neutral | Slightly more formal |
Quick Quiz
“All the runners started at the same time.” Which fits?
- a) 走者たちが同時にスタートした
- b) 走者たちが一斉にスタートした
- c) Both are natural
Answer: c) Both work — 一斉に emphasizes the unified group start.
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