请高手帮我解释下这两句话的不同！谢谢了

Question

if i had told those impossible to you，you should make a very big mistake.
if i had told those impossible to you，you should have made a very big mistake
为什么if从句都是一样的，主句可以不一样，请高手帮我解答下，小弟谢谢了

Answer 1

if 的条件从句分为真实条件从句和虚拟条件从句。
而真实条件从句适用于主将从现，是假设有可能发生的。而虚拟条件从句是假设不太可能发生的。
IF的虚拟语气有三种：

内容 从句 主句
与现在事实相反 动词过去式（be用were） would/could/should/might+动原
与过去事实相反 had+动词过去分词 would/could/should/might+have+动分
与将来事实相反 should/were to+动原 would/could/should/might+动原
下面三句依次是上面三种情况的例句：
If i were you ,I would/could/should/might do that.
If i had know that yesterday,I would/could/should/might have told you .
If it should rain ,the crops would/could/might be saved.

就这样，不是很难懂的