if从句表示与现在或将来事实相反的假设时，不分人称一律用were，这是正式语体。但在非正式语体，当主语为单数一、三人称时，可以用was而不用were. 此时意义完全相同，只是语体有差异。
不过，if I were you, 和as it were这二个结构中的were不可以用was替换。
1、与现在事实相反的虚拟
What would you do if you won the lottery?
2、与过去事实相反的虚拟
If you had been here yesterday, you would have seen her.
3、与将来事实相反的虚拟
If it were to rain/should rain/rained tomorrow, our plan would be put off.
扩展资料
虚名词性从句的虚拟语气
含有should +V的用法，这一部分主要是有关建议和命令的相关从句，包括主语从句，宾语从句，表语从句，同位语从句以及以之相关的形式主语宾语之类的从句。
记忆口诀：一个坚持(insist)，两个命令(order, command)，三个建议(suggest, advise, recommend)，四个要求(ask, require, demand, request)。
1、宾语从句的虚拟语气
He insisted that the meeting be put off.
2、表语从句的虚拟语气
My suggestion is that we (should) stay here for a rest.
3、同位语从句的虚拟语气
There is no suggestion that she (should) resign.
4、主语从句的虚拟语气主要体现在It做形式主语的三种情况： It’s +p.p +that ； It’s + adj. +that； It’s + n. +that
不过，if I were you, 和as it were这二个结构中的were不可以用was替换。
1、与现在事实相反的虚拟
What would you do if you won the lottery?
2、与过去事实相反的虚拟
If you had been here yesterday, you would have seen her.
3、与将来事实相反的虚拟
If it were to rain/should rain/rained tomorrow, our plan would be put off.
扩展资料
虚名词性从句的虚拟语气
含有should +V的用法，这一部分主要是有关建议和命令的相关从句，包括主语从句，宾语从句，表语从句，同位语从句以及以之相关的形式主语宾语之类的从句。
记忆口诀：一个坚持(insist)，两个命令(order, command)，三个建议(suggest, advise, recommend)，四个要求(ask, require, demand, request)。
1、宾语从句的虚拟语气
He insisted that the meeting be put off.
2、表语从句的虚拟语气
My suggestion is that we (should) stay here for a rest.
3、同位语从句的虚拟语气
There is no suggestion that she (should) resign.
4、主语从句的虚拟语气主要体现在It做形式主语的三种情况： It’s +p.p +that ； It’s + adj. +that； It’s + n. +that