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This sentence is in my JLPT textbook:


I thought that it meant something like, "with an unintentional slip of the tongue, my lie was exposed." However, the sentence is marked as being an incorrect usage of すべる, and it doesn't explain why.

I know that one can say つい口{くち}がすべる, which in English I would equate with "a slip of the tongue," to accidentally say something one didn't intend to say.

In Japanese, is it only mouths that slip, not tongues?

(A helpful answer would not only confirm this with a yes or no, but ideally offer a little insight on how 口{くち} and 舌{した} differ in metaphorical terms.)

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Can you explain why tongues slip in English, but mouths don't? I can't. Perhaps it's similarly difficult to ask why the reverse is true in Japanese. – snailboat Mar 12 '13 at 16:53
@snailplane: The question is not why, the question is how. – Questioner Mar 13 '13 at 2:58
広辞苑(第5版)には、「舌がすべる: 話の勢いで、言ってはならないことをうっかり言う。口がすべる。」って書いてあります。 – user1016 Mar 14 '13 at 21:32
@Chocolate: It's in a dictionary, but if I said it in everyday speech, would people readily understand it? – Questioner Mar 15 '13 at 2:41
Yes I think people would readily understand it, even if they don't use the phrase themselves. Probably 口がすべる is more commonly used, so some people might think that 舌がすべる is an incorrect usage, but nobody would fail to understand what you're trying to say by that. – user1016 Mar 15 '13 at 23:53
up vote 2 down vote accepted

Probably the reason the book highlighted this is that the set phrase in Japanese, 口がすべる, is easily confused with the literal translation of a very similar set phrase in English, 舌がすべる。

I don't think this points to an overall difference in the metaphorical uses of 口・舌 (see also the word 舌禍{ぜっか}), just one of many cases where caution is needed. I don't know the book so I don't know if this is something they regularly do - it would have been better if they'd added something along the lines of "this is not the collocation you are looking for, try 口がすべる instead".

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Yes - it would seem mouths slip not tongues.

The book is testing your recognition of the expression 口が滑る, trying to throw you off by inserting 舌. (Its probably a common technique for the other questions you are looking at)

The best insight I can suggest for this expression is to look up 口 and 舌 in the dictionary to see how they are used. 口 tends to be used more for words/talking eg:


But it is not hard and fast. There are also expressions about speaking that do use tongue:

舌がもつれて何も言えなかった|I was tongue-tied

よく舌が回るね|〔批判的に〕You really do [go on / talk].

But the main point for this book is to remember uses of 滑る

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