In a manga I am currently reading, one of the character exclaims:

安心しな。秘密に しとく から。

The general meaning of the second part ("I'll keep it a secret") is quite obvious, and it seems that "しとく" (ostensibly derived from し, with a suffix appended) has more or less the same meaning as plain "する". But I am curious about the grammatical (or dialectal?) construct used here, its usage, nuance etc.

The closest to an explanation I could find, was this verb in WWWJDIC:

とく (v5k) to do something in readiness for, to get something (needful) done

... but I must admit I'm still at a loss as to why it would be used as an auxiliary here.

What is the exact nuance (and grammatical origin) of that "しとく" and does the "とく" suffix work with other verbs?

  • 7
    I thought this was a contraction of しておく. I may be off, though.
    – phirru
    Commented Sep 15, 2011 at 4:21
  • 1
    Found this: homepage3.nifty.com/i-yasu/Lesson33.htm Just before the last bullet point there is a list of commonly used verbs which change in spoken language. 話しておく → 話しとく, 飲んでおく → 飲んどく, etc.
    – phirru
    Commented Sep 15, 2011 at 4:29
  • The first part of the line should be 安心しな (this is actually what Ichinose-san said to Kyoko-san), 心配するな, 心配しなさんな, or the like.
    – yibe
    Commented Sep 15, 2011 at 5:12
  • @yibe: you're right. Was typing from memory. Edited to the correct version (though this doesn't really affect the question at all).
    – Dave
    Commented Sep 15, 2011 at 5:32
  • 2
    (1) It is しておく, and おく is (briefly) explained in japanese.stackexchange.com/questions/2997/…. (2) The example before the edit (in revision 1) was extremely confusing, so even though the edit is not about the part being asked, it was good you edited it. Commented Sep 15, 2011 at 12:15

1 Answer 1


しとく comes from しておく, which in turn comes from して置く. The literal translation of して置く would be, "do it, and then put [the results]". Basically it describes the act of doing something and storing the result of that so that when that result becomes useful, you can use it.

This literal meaning changed overtime (I presume) and しておく became to mean "do something to prepare for something that might happen". In case of 秘密にしておく, the speaker is saying that he/she will keep it secret in case it turns out whatever thing they were discussing indeed needed to be kept secret. I guess it makes some sense, as you could think that the state of that thing being kept secret, is "stored" or "put" somewhere, and then it turns out that that state was useful, or something like that.

The nuance further changed (I presume!), and it became ok to use it almost as a softner. For example, a Japanese speaker might say 今日飲んどく? instead of 今日飲みに行く?. Technically it still means to drink "just in case", but here it's just used to soften the speech. 秘密にしておく could also be a softner, depending on the context.

え、また泥酔して記憶なくなったの? 大丈夫!秘密にしとくから(笑)
    -> Softner
    -> Let's keep it secret for the time being, in case it it wise to keep it as a secret.

しておく is frequently used with とりあえず, which translates to "for the time being".


Both are ok, while the latter is colloquial.


Above is another example. しとく is more frank/colloquial form of しておく.

~おく can also work with other verbs. Here are some examples:



Apparently it's even more complex than that. Here is a Japanese paper on ~ておく's meaning.

  • 2
    Even though historically the auxiliary verb おく comes from the verb 置く, when you consider within present Japanese, they are different. In correct writing, it should not be written in kanji as 置く, and it does not literary mean 'put' anymore.
    – user458
    Commented Sep 15, 2011 at 7:18
  • Thanks for your thorough answer. But I'm still quite unclear on how this affects the meaning of my example sentence above. "Keep it a secret and store the results for later" doesn't really make much sense...
    – Dave
    Commented Sep 15, 2011 at 11:02
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    @Dave: I added a bit in my edit. Also I found a full paper on ~ておく. Basically it lists more functions of ~ておく and discusses its nuance in depth. Commented Sep 15, 2011 at 13:05
  • Thanks for all the precisions... Just to conclude, couldn't しとく/しておく (particularly in my example above) simply be translated by "do... just in case"? e.g. "I'll keep it a secret, just in case"
    – Dave
    Commented Sep 17, 2011 at 3:40
  • @Dave: Yeah, I think so. Commented Sep 17, 2011 at 4:36

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