Grammar JLPT Level N3 - Lesson 9

Structure of 事(こと)がある:

Verb［る］⁽¹⁾ + こと + が⁽²⁾ある
［い］Adjective + こと + が⁽²⁾ある
［な］Adjective + な + こと + が⁽²⁾ある

⁽¹⁾ Verb［ない］
⁽²⁾ も

Details about 事(こと)がある:

ことがある is an expression in Japanese that combines the noun こと with the case marking particle が, and the う - Verb, ある. It is often translated as 'to be possible', 'to occasionally occur', or 'to sometimes occur'. However, the more literal translation of ことがある is '(A) is a thing that exists'.
ことがある may be paired with the attributive form of any other word.

この馬(うま)は人(ひと)を蹴(け)ることがあるので、馬(うま)の後(うし)ろに立(た)たないで下(くだ)さい。
This horse kicks people sometimes, so please don't stand behind him.
タナカ先生(せんせい)の授業(じゅぎょう)はたまに楽(たの)しいことがある。
There are times where Mr. Tanaka's classes are fun.
仕事(しごと)はだいたい大変(たいへん)だけれども、たまには楽(らく)なことがある。
Work is usually difficult, but there are times where it is easy.

Occasionally, が may be replaced by も. In these situations, it implies that '(A) is also a thing that exists'. Basically this just highlights that (A) is something that needs to be considered (among other things).

仕事(しごと)は楽(たの)しいけど、大変(たいへん)なこともある。
Work is fun, but there are times where it gets difficult.
先生(せんせい)はいつも怒(おこ)っているけど、優(やさ)しいこともある。
Our teacher is always angry, but there are times when he is nice.

事(こと)がある

Usage Notes for 事(こと)がある:

ことがある differs from たことがある (a phrase commonly paired with the past form of verbs). たことがある highlights a single event in which the (A) verb was completed. However, when the verb is not in past form, it simply implies that there are 'times' when the verb happens, as opposed to a single/specific time.

週(しゅう)に1回(かい)のペースでラーメンを食(た)べることがある。
There are times when I go to eat ramen once a week.
このラーメンは食(た)べたことがあると思(おも)う。
I think I have eaten this ramen before.