I’d break it down like this
見たことがない
something not seen before
ものがある
to have something
→ = to have something not seen before
Well, you can break it down further. But, the important thing here is to see 見たことがない as a whole to parse.
I’d break it down like this
見たことがない
something not seen before
ものがある
to have something
→ = to have something not seen before
Well, you can break it down further. But, the important thing here is to see 見たことがない as a whole to parse.