happen有偶然发生，出现等含义。是不及物动词,不能用于被动语态。泛指一切客观事物或情况的发生，强调动作的偶然性。
1.表示“某地(某时)发生了什么事”,常用“sth.+ happen +地点/时间”这一结构来表达,此时主语应是事情.例如：
The story happened in 1998
.这个故事发生在1998年。
An accident happened in that street.
那条街上发生了一起事故。
2.表示“某人出了某事(常指不好的事)”,要用“sth.+ happen+to sb.”这一结构来表达.例如：
A car accident happened to her this morning.
今天上午她发生了交通事故。
What happened to you?你怎么啦?
3.表示“某人碰巧做某事”,要用“sb.+ happen+ to do sth.”这一结构来表达.例如：
I happened to meet a friend of mine in the street yesterday.
昨天我碰巧在街上遇到了我的一个朋友。
4.happen表示“碰巧或恰巧发生某事”时,还可用“It happens / happened that...”这一结构来表达。例如：
It happened that Brian and Peter were at home that day.
碰巧那天布莱恩和彼得在家了。
It happened that he had to take part in a meeting that afternoon.
碰巧那天下午他不得不参加一个会议。
注：that从句中的主语是人时,此种结构可以与“sb.+ happen + to do sth.”结构互换。例如：
It happened that Brian and Peter were at home that day.
= Brian and Peter happened to be athome that day.
5.happen为短暂性动词，不能与表示一段时间的状语连用。
