GRAMMAR DETAIL

たことがある

have done before

Follows the past form of a verb to express an experience someone has had at some point up to the present.

Examples

北海道で雪祭りを見たことがある。

I have seen the snow festival in Hokkaido.

子どものころ、海で泳いだことがあります。

I have swum in the ocean before, when I was a child.

Structure: A verb's た form is followed by ことがある.
Basic usage: 北海道で雪祭りを見たことがある。 states the experience of seeing a snow festival in Hokkaido.

Experience and reporting one event
- 去年北海道へ行った reports an event last year; 北海道へ行ったことがある foregrounds having that experience. The experience construction alone does not specify an exact count or date.
No experience and occasional occurrence
- 行ったことがない states a lack of experience of going. The dictionary form in 遅れることがある instead describes occasionally being late, so distinguish the attachment.