ことである in Japanese grammar


Do こと **で** ある and こと **が** ある mean the same thing?




I don't think so.

`である` is basically equivalent to `だ` or `です` (the copula), so `ことである` can be
replaced by `ことです`/`ことだ` where `こと` is either nominalizing the preceding
expression, or is used as literal "thing/fact".

> これは大事なことだ
>
> This is an important matter.
>
> 大事なことがある
>
> [I] have something* very important. ( _lit._ A very important thing exists.)

*Note: unlike similar `もの`, `こと` refers to intangible things.

Additionally, `ことがある` (or polite `ことがあります`) can describe either an event that
happened in the past (with past form verbs), or something occurring with some
regularity (with non-past forms).

> ～に何度か行ったことがある  
>  [I] have been to ~ several times

This usage usually describes personal experience.

It cannot be replaced by `ことです` to express the same meaning.

> ～に何度か行ったことです
>
> Fact of the matter (?) is that [I] went to ~ several times*

*I'm not very sure it's a correct translation.

See also [The different usages of
ことがある](https://japanese.stackexchange.com/questions/3977/)

References: _A Dictionary of Basic Japanese Grammar_ by Seiichi Makino,
articles on **aru 1**, **koto 1**, **koto 2**, **koto ga aru 1**, **koto ga
aru 2**

