I've come to see [突然]{とつぜん} as "sudden in an almost overwhelming manner". The other two, however, I am unable to figure out. What are the differences between these words, and when is one more appropiate than the other?

  • This reminds me that I still don't know the difference between 突然 and 唐突. Jan 4, 2014 at 3:50

3 Answers 3


I'm not sure I agree with the formality distinctions since I hear all of them used in a variety of situations, but that is neither here nor there. As I don't have a true native's insight I will cite some materials produced by natives on the subject.

This question is succinctly answered in this alc entry. To summarize, it says the following:

  • They all mean roughly the same thing, and in the sentence 「子どもが○○飛び出してきた」 any could fill the blank and be acceptable.
  • In the sentence "第一問からいきなり詰まってしまった。" いきなり cannot be replaced with either of the other two. There is a nuance here of beginning an action without proper precaution, of starting something without the expected timing or process. The others do not have this nuance.
  • For the other two, consider the sentence バスが突然急に停まった。 急に describes the way in which an action is carried out. 突然 on the other hand can be thought of describing what's going on (出来事の生じる様子 as the article states it).

That difference is a little abstract and hard to understand though, so I will cite some examples from the explanation written here:

These sentences can naturally use both:

例11)急に/突然 雨が降ってきて、あわてて建物の中に入った。
例12)さっきまで楽しく歌っていたと思ったら、急に/突然 泣き出した。

The following feel more natural with 急に rather than 突然:


The explanation provided is that 急に represents something that changes in a short time while 突然 is something unexpected that happens quickly. In 13 and 14 突然 could be used, but since getting taller or a team getting stronger are more of a process of change (変化の過程), 急に is better. To quote fully, they are summarized as this:


And for my last copy/paste job, one more example:


So your daughter suddenly got sick. With 急に it means that she went from a healthful condition to an unhealthy condition in a short period. With 突然 it's like saying she suddenly fell ill as if out of nowhere.

I'm not exactly sure how they want to reconcile this idea of a process of change with the acceptability of the sentence "急に飛び出した." It could be that there is generally an overlap but in certain contexts these nuances kick in. Dictionaries don't provide much help since they all have each other in their definitions. Ultimately they're all basically the same and you probably don't need to worry too much about looking dumb if you make a mistake or something.


いきなり is casual and very colloquial.

突然 is more formal, seen in writings often but still fine for colloquial use. Same as いきなり in meaning.

唐突 is the same as 突然 but used with human behavior, not inanimate objects, trains, astroids, etc. Example: 唐突なカミングアウト (unexpected and sudden coming out of a person about something).

急に is focused on sudden in meaning, nothing to do about surprise.


One difference is in place of usage. As you may know, a typical pattern (with certainly plenty of uncorrelated exceptions) is for "natural" Japanese words like いきなり to be favored in oral/informal contexts, whereas imported 漢語 appears more often in written/authoritative contexts. If you use 漢語 all the time in your speech, your friends may tell you you sound like a book ;)

Examples (from "hard" written language to spoken):

  • 現在 -> 今
  • 柔軟性の高い -> 柔らかい
  • 不得意 -> 苦手 (here it matters that にがて is pronounced with 訓読み)
  • 流暢 -> ぺらぺら
  • 迅速 -> 速い
  • 遭遇する -> 遭ってしまう
  • 到着する -> 着く
  • 運搬する -> 運ぶ
  • 切断する -> 切る
  • 驚愕 -> 驚き
  • 教育方法 -> 教え方
  • 構成 -> 成り立ち
  • 翌日・明日《みょうにち》 -> 明日《あした》

The above all mean something slightly different, but can replace each other in most cases, changing the tone.

With that in mind, 「いきなりなんなのよ!」 「急に寒くなったね」 (oral) and 突然、雨が止《や》んだ。(written) would I think be representative uses for each of these words.

As for "sudden in an almost overwhelming manner", I think you can get that from any of these three.

  • reason for downvote on both of these answers? I can easily present about fifty cases to support mine. I'll edit it to include some. Jan 4, 2014 at 20:06
  • From reading you answer, I feel my question is still left unanswered. Furthermore, I have heard 突然 used in casual situations, which inclines me to believe the answer is not as simple as you attempt to portray it. Jan 5, 2014 at 1:31
  • True, I didn't answer your whole question authoritatively, because I don't think there is a wholly satisfactory answer. Usage is incredibly complex, and "rules" are broken often deliberately to create an effect or accomplish a tertiary task. Let me ask you this: What's the difference between "sudden" and "abrupt"? Does your answer apply in all situations and all locations where English is spoken? Jan 5, 2014 at 2:44
  • Of course I cannot setup a rule that will explain every single situation, however, something that aids understanding in the majority of cases can be setup. Your answer simply boils down to "Oral vs Written" which I, judging from what little I've seen, can't believe. Jan 5, 2014 at 11:55

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