I know what する means in terms of basic usage and obvious usage... I've been studying for a while so like, this isn't going to be a "What's 1 + 1" question hopefully.

The question is to do with how する works with adverbial forms. What is the image you get in your head when someone says like 口にする or 気にする or ようにする or 下にする or 深くする. See I have trouble understanding how する should be envisioned. Is it the sense of doing towards that state represented by the adverb... or is it the sense of doing する in the way of that adverb?

For example, 口にする seems to be like "DO WITH MOUTH" since it means both talk and eat but why not 口でする then if that's the case? And 下にする is like.. different.. it doesn't feel like で but rather toward.... Are these two different に's or two different する's?

I mean... think about Aにする... People often say like it means to "do towards A" but recently I realised it is short for B を A にする...

So what is this する thing then? Is it an action? Is it a stand in for the flow of your life and how it progresses?

  • I think it is a stand in for the flow of my life and how it progresses.
    – Earthliŋ
    Oct 29, 2013 at 21:23
  • Are you being serious? If so could you give some evidence to your assertion?
    – Nathan
    Oct 30, 2013 at 0:11
  • 口にする is a fixed expression, so applying one of the usual meanings of に to it won't work. For example, 口腔 also means mouth, but 口腔にする does not mean the same.
    – dainichi
    Oct 30, 2013 at 0:33
  • Ok, but like, where does that leave everything else? What is the standard interpretation of X に する?? What is happening to X?
    – Nathan
    Oct 30, 2013 at 1:24
  • 1
    Basic words often have many meanings which are only loosely related, and this should not be surprising if you consider the meanings of basic words in English such as make and take. You can check dictionaries for different meanings of する (Daijisen lists 15 meanings), but it is probably more useful to learn them as you encounter the word in text. By the way, 口にする uses に because it means “bring to mouth” rather than “do something with mouth.” Oct 30, 2013 at 1:27

1 Answer 1


I would suggest that you think of する and なる as a pair.

する expresses an active human effort in performing an action. It focuses on the process of the action.

なる focuses on the result. Unilke する, a human effort may or may not be an essential element in the process leading to that result.

To take the phrases you listed ( 気にする or ようにする or 下にする or 深くする) for example, all of them still make sense if the する part is replaced with なる even though the meanings will change.

As others mentioned above, you should not include a set phrase like 口にする in the list. 口する, by the way, means something I am not allowed to explain in public. You decipher that one using what I said about "human effort".

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