こと

In a sentence

• ピアノを弾くことが好きです。

  I like playing the piano.

  Here, the particle 'こと' nominalizes the verb '弾く' so that it can function as a noun (playing).

• 雨が降ることを知らなかった。

  I didn't know that it would rain.

  In this sentence, 'こと' is used to refer to the occurrence or fact of raining, serving as a conceptual marker for the action.

• 旅行のことを考えています。

  I am thinking about the trip.

  Here, 'こと' refers to matters or things related to '旅行' (trip), emphasizing the concept of the event or situation.