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A couple of times I've tried to say "I agree with..." or "he agrees with..." but I don't know whether I'm using 同意{どうい}する correctly.

In what ways should に同意{どうい}している be used? Also, which particles should be used? Can only be used before 同意{どうい}する or are there circumstances where other particles are used as well, such as and ?

In many examples I've found using 同意{どうい}する, I've seen (だ)ということに or just (な)ことに (the / after na adjectives/nouns and without / after i adjectives/verbs it seems.) Is there a specific reason for using one over the other, e.g. is the longer (だ)ということに more polite, and what do these mean?

Some example sentences:

  • I agree with his opinion:


  • I agree with him that oranges are tasty:


  • He agrees that apples are tasty:


  • Many people agree that brussel sprouts don't taste nice:


See also: What are the different ways of saying to agree or disagree with a person? for other ways of agreeing/disagreeing with someone.

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I think 賛成 has the added meaning of "approve" – Flaw Oct 16 '11 at 3:26
I think a common one is 同感【どうかん】. It seems to be a little "softer" and more familiar than 同意【どうい】. – istrasci Oct 16 '11 at 3:39
The example オレンジはおいしいだということに彼に同意します is totally ungrammatical. 芽キャベツはおいしくないだということに同意する人が多い is ungrammatical unless you are referring to some non-standard dialect. – user458 Oct 16 '11 at 5:36
For オレンジ..., you cannot have two ...に phrases. Remove either. And for the two sentences that I mentioned, remove だと. – user458 Oct 16 '11 at 7:53
@DavidMorrissey Your editing is right. I should have said to remove . Sorry. – user458 Oct 16 '11 at 15:50

You can find a lot of examples here http://eow.alc.co.jp/%E5%90%8C%E6%84%8F/UTF-8/?pg=1 (you may want to check later pages), which will explain a lot.

It seems that we do use "に" for "同意する".

"ということ" literally means "the so-called", which I think is a little more polite.

Also to @sawa , search int the above site with "いという" and "いだという" (I know they are not words nor phrases ...) gives interesting results. It seems that wile i adjectives, "美味しいだということ" can be used.

And I think "オレンジはおいしいということ彼かれに同意どういします" is still a little wired, maybe it should be "オレンジ**おいしいだということ*について*彼かれに同意どういします。". A phrase with nothing in the end doesn't sound natural. (About "は" and "が", I just feel this way, I am not able to explain it in details.)

BTW, I am not native, so correct me if I am wrong.

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