虚拟语气If I were U

题目

虚拟语气If I were U
都说If I were U 是对现在的假设,那么他可以表示对过去的假设吗?
例：
If I were U,I would have stopped that guy.
如果我是你（表示对过去某一时刻的假设）,我就会阻止他了.

答案

不可以,
条件句中用动词过去式(be 用 were)时,可表示将来和现在的虚拟,但是不能表示过去.
对过去的虚拟,可改为：
If I had been there,I would have stopped that guy.