How to tell them apart
途端に focuses on the exact moment right after a completed action, and the second clause is an unexpected past event, as in ドアを開けた途端に猫が飛び出した. かと思うと expresses the speaker's surprise that a second event followed the first with almost no interval, as in 雨が降り出したかと思うとすぐやんだ. The two overlap in showing rapid succession, but 途端に highlights the instant itself while かと思うと highlights the observation of quick change.
- 途端（に） Use 途端（に） to describe what happened in the very instant right after an action was completed.
- かと思うと Use かと思うと to describe two observed events in quick succession with a no sooner than feeling.
| Grammar point | Meaning | JLPT level |
|---|---|---|
| 途端（に） ni | the very instant something happens; right after doing something | N2 |
| かと思うと kato uto | as soon as; no sooner than | N2 |
途端（に） ni
the very instant something happens; right after doing something
途端に expresses that one event happens in the very instant a completed action occurs, often highlighting a sudden or unexpected result. It attaches to the plain past form of a verb, as in 聞いたとたんに or 触れたとたん, with に optional and no change in meaning. The second clause must describe something that actually happened and cannot express a command, request, or speaker intention.
-
そのニュースを聞いたとたんに彼女は真っ青になった。
On hearing the news, she turned pale.
-
女の子達は彼のジョークを聞いたとたんに笑い出した。
The girls burst into laughter when they heard his joke.
かと思うと kato uto
as soon as; no sooner than
かと思うと expresses that one completed event is followed almost immediately by another, often with a sense of surprise at how quickly things changed. It attaches to the past ta-form of a verb, as in 着いたかと思うと or 止んだかと思うと. Both clauses describe realized events in sequence, so the second verb is normally in the past tense and the interval between them is very short, not a long span like overnight.
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電車が着いたかと思うと、すぐに出発した。
No sooner had the train arrived than it left again.
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雨が止んだかと思うと、また降り出した。
No sooner had the rain stopped than it started falling again.
途端（に） and かと思うと are both JLPT N2 grammar points that Japanese learners often mix up. This page compares them side by side on meanings, usage and example sentences, so you can tell them apart.