Who knows the difference between 忘れてた and 忘れちゃった? In what kind of situations you use each of those?


ちゃう is the shortened form of ちまう. Which is the shortened version of 〜てしまう. The definition from the link above is:







2 終わりになる。終わる。「予定より仕事が早く―・った」「今年は花見をせずに―・った」

3 使用したもの、大切なものなどを元の場所や入れ物などの中に納める。かたづける。「夏物を―・う」「雛人形を―・う」「胸のうちに―・っておく」

4 信用取引や清算取引で、建玉(たてぎょく)を転売または買い戻すことによって取引を完了する。

㋐ないようにする。なくする。 「世の中には富(=富クジ)で身代を―・ふもあるから」〈黄・金生木〉

㋑精算する。特に、年末の決算を済ます。 「留守のうちに手廻しよく、内証―・ひ置きけるとうれしく」〈浮・胸算用・五〉

㋒殺して結末をつける。 「ほかに―・うてやる思案もあり」〈浮・二十不孝・一〉

㋓遊里で、一定の時間や紋日に揚げ代を出して遊女を買い切る約束をする。 「あしたあの八右衛門めが―・って下の魞(いけす)へ手めえを連れていくさうだ」〈洒・娼妓絹籭〉

6 (補助動詞)主に動詞の連用形に接続助詞「て」を添えた語に付く。



In this case, it's the 6th definition ㋑ that ちゃう represents, "Implying that something unexpected happened".

So if you say 忘れてた it means, "I forgot". But わすれちゃった means "I forgot having unexpected consequences".

In my experience, using ~てしまう or ~ちゃう is more of a "whoops!" sort of comment, whereas 忘れてた is more of a statement of fact. "Do you remember coming here as a child?" would be more of the latter, while waiting in line for a baseball game and realizing you forgot the tickets would be more of the former 「チケットを忘れちゃった!」

In general, the use of either ~ちゃう or ~てしまう when referring to a personal screw-up is incredibly casual and not appropriate for work settings (you would generally apologize first, as it comes off a bit too light-hearted and as if you don't take the mistake seriously.

  • 1
    Personally, I can't upvote this answer because copying and pasting from a Japanese dictionary isn't all that helpful. A person who is able to read through that much Japanese text in a Japanese dictionary is unlikely to need to come to JLU to ask questions about basic things like what ~ちゃう means. The explanation at the bottom is helpful, but it's hindered by the assumption that people have already differentiated the "6th definition" from others before getting there. – Questioner Jun 30 '13 at 2:03
  • @DaveMG Feel free to improve on my answer either with an edit, or with a better version of your own. The goal is not upvotes, but answering the question. If mine does a poor job, you're better served creating a better answer than a snide remark in the comments, no? – jmac Jun 30 '13 at 2:35

They're mostly the same, but 忘れちゃった has more of a sense of 'whoops' than just plain 忘れてた. I'd probably be more likely to use 忘れちゃった in a situation where the forgetting something had some kind of negative consequence (though probably a small one, as it's not a particularly formal form and it tends to have a sense of downplaying the consequences - if you really screw something up by forgetting something, you'd want to go the distance and say 忘れてしまいました.) It sounds kind of weird to use 忘れちゃった to mean something was forgotten but nothing bad came of it.


I think the important thing here is to understand the word しまう,and then to understand that ちゃう is the colloquial contraction of shimau. For simplicity's sake, I'll just write everything in romaji.

Shimau: Means to "completely" do something. Yatteshimau zo! means something like "I'm going for it!" It can have some sense of daring or regret associated with it. Little kids say "chau" all the time ("nichau yo", "I'll cry!), and parents use it to scold them: "Naicha dame da yo!" ("Don't you cry!"). In any case, shimau is used frequently (in both formal and informal speech and writing) and chau is also used frequently, albeit in speech. It is interesting to note that if you add the conditional "-ba" to the end of "-shimau" ("shimaeba") then it becomes more of an challenge or proposition of difficulty ("wasurete shimaeba" = "if you can manage to forget").

So, to answer your question, when used with wasureru, the only real way to interpret wasurete shimau is to see it as a statement of regret at having forgotten or unintentional forgetting, and "wasurechatta" means something similar although would not be said in quite the same circumstances.

This is in contrast to "wasureteta" which is a contraction of "wasurete ita" (sic "I had forgotten") which implies that you had forgotten but that someone or something just reminded you of that. The difference between "wasureta" and "wasureteta" is like the difference between "I had forgotten" (which implies that you now remember) and "I forgot."

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    ちゃう is a contraction of て plus しまう. The ちゃ in 泣いちゃだめだよ is not from しまう, but from て plus は. – snailcar Jul 3 '13 at 10:24

忘れてた means 'I forgot', but it carries a sort of 'continuous' meaning, i.e. somebody has forgotten something for a period of time. At least that's how I've come to understand it.

On the other hand, 忘れちゃった is a colloquial, shortened version of 忘れてしまった.

~てしまう is a verb-only conjugation and has three basic meanings, which are:

  1. The action expressed by the verb was done unintentionally, by accident.
  2. The action was done completely, finalized.

In this case, 忘れちゃった may mean both, as in:

Whoops, I totally forgot.

  • The question is about 忘れてた and 忘れちゃった, not about 忘れた and 忘れちゃった. – l'électeur Dec 24 '13 at 12:18
  • You're right! I don't know how I missed that :) Editing accordingly. – Ch1mp Dec 24 '13 at 12:26

忘れちゃった you forgot and there was a consequence to it.

忘れてた does not imply consequence.

  • Does anyone on this site with points actually live in Japan and use Japanese on a daily basis? I'm beginning to think the only people with points enough to downvote are bored academics who've never used Japanese. – Jon Jan 4 '14 at 12:27
  • 日本人は、いつもいる人は少ないけど(最近は2人くらい。)、たまに来る人なら数人います。日本語話者じゃなくて日本に住んでる人は、結構いっぱいいます。ところでダウンボートしたの私じゃないです。 – user1016 Jan 4 '14 at 15:30

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