Can one use ことにする to express the idea "A decides that B will do X"?

Take the sentence 私は外へ出ることにした. The way I see it, 私 is the subject of both 出る and した, with one usage omitted due to being understood. So in full the sentence is

I decided to go outside.

Now what happens if the subjects are different? Can we say

A decided that B would go outside.

If this construction is not allowed, how else could you say this?

  • 1
    I think you need to amend your question to "How does one say: "A decided that B will do X". Can one use the expression 「ことにする」? (「ことにする」is used to say "A decides to do X", 「ことになる」is used to say "It was decided that A will do X". You are going one step further.)
    – Tim
    Oct 12 '13 at 15:15
  • 1
    AはBを外に出すことにした would be more natural.
    – jovanni
    Oct 14 '13 at 16:59
  • Yes, @jovanni is correct. You are looking for the causative form of a verb, in which one party is made to do a verb because of another party.
    – user4060
    Oct 15 '13 at 21:16

I think one of your assumptions is wrong. A nominalized verb phrase doesn't necessarily need a subject (omitted or otherwise). Take a look at the following sentence:

[ 嘘をつくこと ] は良くない。
[ Telling a lie ] is not good.

I don't think there's a recoverable subject in the verb phrase 嘘をつく. I think it's more like "telling a lie" or "to tell a lie" than "[someone] tells a lie". And I think the same thing is true about your example:

私は [ 外に出ること ] にした
As-for me, [ going outside ] decided-to
= I decided [ to go outside ].

The nominalized verb phrase [ 外に出ること ] talks about the idea of going outside, but it doesn't specify an actor via a subject or anything else. There's no subject to recover here.

The topic 私 connects to the matrix verb した, not the embedded verb 出る. Usually a topic splits things into two parts:

私は | 外に出ることにした
topicは | comment

This is called a topic-comment structure: the comment on the right tells us something about the topic on the left. Essentially, the topic connects with the entire verb phrase on the right half, the head of which is した. And that's why it can't connect with 出る, which is stuck inside a relative clause.

If you'd like to say you decided to make someone go outside, you can do so by getting rid of the intransitive 出る and putting the transitive (causative) 出す in its place (as jovanni suggested in this comment). This makes an を-role available inside the nominalized verb phrase:

私は [ snailboatを外に出すこと ] にした
As-for me, [ making snailboat go outside ] decided-to
= I decided [ to make snailboat go outside ].

But you can't directly say "A decided that B will do X", only "A decided to make B do X". The ことにする idiom doesn't have a separate role for B to fill.

(Note: in the above, decided-to really corresponds in meaning to ことにした, not just にした. Even though ことにする isn't a single constituent, it is a single idiom, so you can't really divide it up when talking about what it means.)

  • I believe you are correct. I recall reading one study on the effect of language on the ability to acquire verbs and nouns from language. The study showed that Japanese children tend to have a harder time disassociating the object and subject from a verb. Overall, that implies that in Japanese, a verb contains the subject and object, even when they are not explicitly mentioned. In English, the nouns are perceived as separate from the verb.
    – user4060
    Oct 15 '13 at 21:21

I would like to add some intricate points to snailboat’s answer.

Snailboat is right in that in general, verbs in Japanese do not have to have a subject, even an implied one. Also it is right is to say that we cannot use ~ことにする to state someone decides that someone else will do something. ~ことにする is used when someone decides what he/she will do.

However, there are cases where BがXすることにする sounds fine to me.

As you might be aware, the sentence

(1) 私は私が外へ出ることにした。

is unnatural. However, if there is some context where who goes outside is important, then it makes sense to say:

(2) 私は自分が外へ出ることにした。 I decided that I would go outside.

For some reason, it is strange to repeat the topic and the subject as in (1) even when who goes outside is important.

As another example, suppose that a team of athletes discussed the running order in an upcoming relay race. Then it is fine to say:

(3) 話し合いの結果、康介がアンカーを務めることにした。 As a result of the discussion, they decided that Kosuke would run as the anchor.

The subject of 務める is 康介 and it is explicitly stated. The semantic subject of 務めることにする is the team, and it is not explicitly stated but implied by the context.

(I think that there is another interpretation of (3) depending on the context. See the remark after sentence (5) below.)

If we say

(4) 話し合いの結果、康介にアンカーを務めさせることにした。

then I think that it means that Kosuke was not one of those who decided it. Probably he was not at the discussion, or he participated in the discussion but he did not agree to the decision.

By the way, if we change が to は in (3) and say

(5) 話し合いの結果、康介はアンカーを務めることにした。

then it is more likely to mean “As a result of the discussion, Kosuke decided to run as the anchor.” That is, 康介は specifies the topic of the whole sentence rather than just the subject of the アンカーを務める part.

It is also possible to interpret 康介が in (3) as the subject of the whole アンカーを務めることにした part. In this case, (3) means roughly the same thing as (5), with an emphasis on the subject: “As a result of the discussion, it was Kosuke who decided to run as the anchor.” Therefore sentence (3) may be ambiguous depending on the context. But given that it was a result of the discussion, I think that it is more natural to interpret that the team decided it unless the context implies otherwise.


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