I came across the following sentence in chapter ten of "Dragonwings" by Laurence Yep:
"They looked shocked, as if not believing that all of this could happen to them. I could not help remembering what fine houses and mansions had once been there, and …"
I have a problem with "could happen" in this context. I believe it should be "could have happened".
Here is an example sentence that I found in a similar context, and it is from a reliable source: BBC Home:
"Later in the evening small groups of older folk wandered around not quite believing that this could have happened in their own town.
Here's a related link.
Best Answer
X could happen means X is believed able to happen because of a past or completed event. We don't know if it will happen, we are just saying it is able to happen.
X could have happened means X was believed able to happen because of a past or completed event. This can be used if we know it happened and we are talking about the past possibility, or if we are not sure it happened and saying the possibility still exists.
There is no could happened.