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
Kanojo no koto wa yoku shitte imasu.
I know her well.

2. After dictionary form of verb/adjective
Kyou wa suru koto ga takusan arimasu.
I have a lot of things to do today.
Miru koto wa shinjiru koto desu.
Seeing is believing.
Yoku yasumu koto ga hitsuyou desu.
It is necessary (for you) to get enough rest.
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
Watashi ga itta koto o kare ni tsutaete kudasai.
Please tell him what I said.
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)
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