虚拟语气的时态如何使用？

Question

虚拟语气过去时、现在时、将来时分别在什么情况下使用？

Answer 1

虚拟即不真实的，所以标准的虚拟语气分三种情况：与现在事实相反、过去事实相反和将来事实相反。
从句时态：往前推一个即可~ 如与现在事实相反的从句用过去时；过去相反的用过去完成时；将来相反的用过去时/should do/were to do ~(注：虚拟语气中的be动词只能用were哦)
主句时态：现在和将来相反都是情态动词+do，过去相反是情态动词+have done（此处的情态动词指的是should could would might）

Answer 2

过去时 I should have bought that shoes. (the fact is I didn't buy)
我应该买那双鞋。（但事实是我没有买）
现在时 I would rob the bank if I had a gun. (the fact is I have no gun)
如果我有枪我就抢银行。（但事实是我没枪）
将来时 I would have bought that shoes after getting my salary. (I do buy that shoes)
我领到工资会去买那鞋。（我肯定会买）

Answer 3

过去时 I should have bought that shoes. (the fact is I didn't buy)
我应该买那双鞋。（但事实是我没有买）
现在时 I would rob the bank if I had a gun. (the fact is I have no gun)
如果我有枪我就抢银行。（但事实是我没枪）
将来时 I would have bought that shoes after getting my salary. (I do buy that shoes)
我领到工资会去买那鞋。（我肯定会买）