if i were you 为什么用were

因为if从句表示不可实现的条件或根本不可能存在的条件，也就是一种虚拟的条件或假设，所以从句多用一般过去时或过去完成时。如：If I were you,I would invite him to the party.如果我是你，我会邀请他参加聚会。

虚拟语气表示说话人的主观愿望、猜疑、建议或与事实不符的假设等，而不表示客观存在的事实。虚拟语气是由句中的谓语动词的特殊形式表示出来的。如：

If I were a bird,I would be able to fly in the air.

如果我是一只小鸟，我就能在空中飞行。

I wish I could pass the examination.

我希望我能通过考试。

Hope you succeed!

祝你成功！

I wouldn’t wear a sweater in such hot weather if I were you.

换做我是你，我不会在这样的大热天穿毛衣。

If I were you,I would explain to Jack what happened.

如果我是你，我会想杰克解释事情的经过。