if 条件句遵守主将从现的原则.
if it is fine tomorrow ,we will go out .如果明天天气好,我们就出去.
虚拟语气表示相反.
表示和现在相反,从句用一般过去时.if i had a big house ,
如果我有一个大房子.我会怎样怎样.（其实没有大房子,和现在的情况相反）
表示和过去相反,从句用过去完成时.if i had won that game.
如果（过去的某一时间）我赢了那比赛,我就怎样怎样.
表示和将来相反,从句用
1.过去时
2.should+do
3.were to do
这三者只有细微差别.
If you succeeded,everything would be all right.
=If you should succeed,everything would be all right.
=If you were to succeed,everything would be all right.
翻译：如果你将来会成功的话,一切都会OK的.
ALL.