第三条件句的结构

这是第三条件句（third conditional），用来讲对过去的设想：本来可能发生、但实际没有发生的事。

结构是：If + 过去完成时，+ would/wouldn't + have + 过去分词。例如：

If I had known about the meeting, I would have attended it.
If she had studied harder, she would have passed the exam.
He would have been happier if he had chosen a different career.
If I had seen you at the party, I would have said hello.