koto こと

Noun and nominalizer meaning: thing (in the abstract sense), ...ing, to (do), (the fact) that

When used to nominalize the preceding clause, the nominalized phrase expresses a fact which is already accomplished or which the speaker supposes will be accomplished. koto tends to be taken as an object by verbs of mental activity such as knowing, recognizing, understanding, hoping, learning, etc.

1. After noun + no
彼女のことはよく知っています。
Kanojo no koto wa yoku shitte imasu.
I know her well.

2. After dictionary form of verb/adjective
今日はすることがたくさんあります。
Kyou wa suru koto ga takusan arimasu.
I have a lot of things to do today.
見ることは信じることです。
Miru koto wa shinjiru koto desu.
Seeing is believing.
よく休むことが必要です。
Yoku yasumu koto ga hitsuyou desu.
It is necessary (for you) to get enough rest.
日本は物価が高いことはよく知られている。
Nihon wa bukka ga takai koto wa yoku shirarete iru.
It is well known that prices in Japan are high.

3. After ta-form of verb/adjective
私が言ったことを彼に伝えてください。
Watashi ga itta koto o kare ni tsutaete kudasai.
Please tell him what I said.
幸子さんがヨーロッパに行ったことを知っていますか。
Sachiko san ga youroppa ni itta koto o shitte imasu ka.
Did you know that Sachiko has gone to Europe?

4. After declarative statement
(used as a command form in written notices)
敷地内に入らないこと。
Shikichi nai ni hairanai koto.
Don't enter the premises.
-> See also: koto ga aru, koto ga dekiru, koto ni naru, koto ni natte iru, koto ni shite iru, koto ni suru, mono, no, to, to iu