假设的语法
英语中表示假设的句子主要是虚拟语气，其表示方式有：
1.以if条件从句为虚拟语气标志：
与现在事实相反 从句时态用一般过去时（be用were),主句用过去将来时
例如：If I were you, I would finish homework first.
与过去事实相反 从句用过去完成时，主句用过去将来完成时
例如：If I had gone there, I would have bought two tickets.
与将来事实相反 从句用一般过去时或过去将来时，主句用过去将来时
例如：If he had/would have time, he would come to your birthday party tomorrow.
2.以even if/though让步从句为虚拟语气标志 主从句时态同if条件从句相同
例如：He might give you more help, even though he were/was very busy.
3.以as if/though引导的表语从句或状语从句为虚拟语气标志 主从句时态同if条件从句相同
例如：It seems as if he had known the news.
应用条件
在表示假想的虚假的、与事实相反的或难以实现的情况时用虚拟语气，表示主观愿望或某种强烈情感时，也用虚拟语气。即当一个人说话时欲强调其所说的话是基于自己的主观想法，愿望，假想，猜测，怀疑或建议，而不是根据客观实际，就用虚拟语气。主要是英语语法的一种表达。
学习英语语法：三种时间的纯假设基本句型。
英语中用得最多的是陈述语气，其次是疑问、祈使语气，只有很少一些场合用虚拟语气。
虚拟语气，主要有4种类型：
1.表示纯假设（非真实条件）
2.表示请求
3.表示命令、要求、建议
4.表示愿望
三种时间的纯假设基本句（以be, do, work为例）：
从句
主句
与现在事实相反
过去时
过去将来时
+were/was…,
If+主语+worked
+were wroking
If she were a bird,
如果她是一只鸟，
If you worked here,
如果你在这工作，
+would/should be…
主语+would/should do
+might/could work
She would fly in the air.
她就会在空中飞翔。
We would discuss together every day.
我们就会天天一起讨论。
与过去事实相反
过去完成时
过去将来完成时
+had been…,
If+主语
+had worked
If we had been careless,
要是我当是时很粗心，
If they had failed last time,
如果他们上一次失败了，
+would/should have been…
主语
+might/could have worked
we would have made a serious mistake,
我们就已犯了严重错误了。
they would have given it up.
他们就会已经放弃了。
与将来事实相反
过去一般时/过去将来时
过去将来时
+were…,
If+主语+worked
+should work
If he were to come back,
如果他以后回来，
If she should fail again,
如果她将再一次失败，
+would/should be…
主语
+might/could work
I would be the first to meet him.
我会是第一个迎接他的。
she might not give up.
她也许不会放弃。
注意：在If I were you中I只能接were,不能接was。但其他人称的代记后不管单复数都接were，单数也可接was.
