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My book says that "koto" can convert verbs into nouns. It can also convert adjectives and adverbial nouns, but what does that mean? It gives examples like:

Tori o tsukamaeru koto wa kantan ja nai?

Watashi wa kare ga nihon e itta koto o nd dare date boku ga atama ga warui koto ot shitteru

The book says "koto" means "thing", "fact", or "matter".

How exactly do you use "koto"?

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I presume your book says that koto is used to convert verbs into nouns, right? – Darius Jahandarie Dec 20 '13 at 3:35
yes what I want to know is how exactly to use it in a conversation – Arturo Dec 20 '13 at 3:39
thank you very much for separating and explaining. Sorry but book also says it converts adjectives and adjectival nouns, how does that work, I understand the nouns now, the other example is watashi wa kare ga nihon e itta koto o nd dare date boku ga atama ga warui koto ot shitteru thanks for your patience sensei – Arturo Dec 20 '13 at 3:59
Hi @Arturo, could you check the spelling on your last example one more time? Some of the words seem incorrect and it makes it hard to understand the example. – Troyen Jan 26 '14 at 9:03

tori wo tsukamaeru
"I catch birds."
"I will catch the bird."

This is a full sentence, as you can see in the English meanings provided.

tori wo tsukamaeru koto
"catching birds"

When you add koto on the end, it becomes a noun.

Since it is a noun, you can use as part of a larger sentence:

tori wo tsukamaeru koto ha kantan ja nai
"Catching birds is not simple."

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There are other meanings of koto -- I only talked about the one you were asking about in this answer. – Darius Jahandarie Dec 20 '13 at 3:45
oh realy do you mind telling me them, if no that's ok I'll look for them on my own, its cause it's not clear yet how to use koto, by your explanation I know you change it to catching, eating, and so on, but thanks anyway – Arturo Dec 20 '13 at 4:03

How about this:

彼女たちは 日本語を 勉強したことが あります。
Kanojo-tachi wa nihon-go o benkyō shita koto ga arimasu.
Them girls studied Japanese at least once.

  • "koto" turns every thing preceding it into a substantive (noun) clause.
  • "ga arimasu" indicates that the subject exists in at least one instance.
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Darius' example above is right. But, you can also use KOTO as follows. Anyone, please correct me if the below translations are wrong.

かのじょ たち は 日本 ご を べんきょう した こと が あり. - She (all) HAD DONE the thing of studying Japanese.

かれ の かお は 見た こと が あり ます. - I HAD DONE the thing of looking at his face.

MP 3 プレーヤー を つかった こと が あり ます か? - HAD you DONE (did you do) the thing of using the MP3 player?

Past tense + koto = HAD DONE THE ACTION OF something.

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I don't think ~たことがある should be translated with the past perfect tense. E.g. 彼の顔は見たことがあります should be more along the lines of I have seen his face (before/already). The past perfect tense seems to fit well for ~たことがあった, though. – Earthliŋ Dec 14 '14 at 12:17

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