What does する mean here?


> So Person A says: `どうしたんですか？`
>
> Person B replies: `忘れ物をしたんです。`

I'm not understanding `した` in this sentence. `忘れ物` means `something left
behind or forgotten`. So I translate `忘れ物をした` as `did forgotten-thing`. Which
makes little sense. So how am I to translate or make sense of `した`'s use here?




する here is a [light verb](https://en.wikipedia.org/wiki/Light_verb), which
means you basically have to memorize which verb should be used with which
noun.

In Japanese, 忘れ物 is a noun which is always used with する, and 忘れものをする is a very
common way to say "forget/leave something". You have to memorize this.

English also has verb usages which are almost unpredictable for learners. In
English you can say "do the dishes" to mean washing dishes, but Japanese
people never say 皿をする. See [this
question](https://ell.stackexchange.com/q/42909/8629), too.




する here is a [light verb](https://en.wikipedia.org/wiki/Light_verb), which
means you basically have to memorize which verb should be used with which
noun.

In Japanese, 忘れ物 is a noun which is always used with する, and 忘れものをする is a very
common way to say "forget/leave something". You have to memorize this.

English also has verb usages which are almost unpredictable for learners. In
English you can say "do the dishes" to mean washing dishes, but Japanese
people never say 皿をする. See [this
question](https://ell.stackexchange.com/q/42909/8629), too.

