1、表示与现在事实相反的情况下会用were
例如:If I were you,I would take an umbrella.
如果我是你,我会带把伞.（事实：我不可能是你）
2..表示对将来情况的主观推测从句用if+主语+were to do
例如:If she were to be here next Monday,I would tell her about the matter.
如果她下周一来这儿的话,我就会告诉她这件事的始末.（事实：来的可能性很小）
虚拟语气中是没有was to这种用法的
不知道这样的回答楼主觉得满意不?有不明白的可以继续问我