Question

I don't know whether you happen to have heard, but I'm going to study in the USA this September

I don't know whether you happen to have heard, but I'm going to study in the USA this September.
我一直在纠结一个问题 为什么这里要说you happen to have heard 而不是 you have happened to hear?

Answer 1

是碰巧已经听说，不是已经碰巧听说，所以have heard 是hear 的完成时，而不是happen的完成时

Answer 2

动词不定式的完成式，表示在谓语动词之前发生的动作，比如：
To have known her is a privilege.
This house seems to have been built by a very good architect.
By 1992, he hoped to have opened a branch overseas.
There is no need to have bought a new pair of shoes for me.
He is too young to have seen the old society.
They might have found him to have lived longer, had a particular circumstance not occurred.
The game was originally scheduled to have taken place in Rome.
i intended to have finished my worked last night.
你给出的句子也是一样，意思是：“我不知道你听说没有，今年九月我要到美国去学习了。”happen表示“碰巧”时，一般不用现在完成时，并且“听说”在说话之前，“碰巧”在后，所以用动词不定式的完成式表示。希望我能帮助你解疑释惑。

追问

碰巧和听说为什么有时间先后呢？应该是同时发生啊？

追答

一般来说，happen表示“碰巧”是不用现在完成时的，但是“听说”是说这句话之前就已经发生的，动词不定式必须用完成式形式，希望我能帮助你解疑释惑。

追问

那是不是hear不是在跟happen比较，而是在跟don't know之间比较时间先后？ 这么理解对吗

追答

对，可以这样理解，希望我能帮助你解疑释惑。