if引导的虚拟语气
If引导的条件状语从句中的虚拟语气：1、表示对过去情况的虚拟：从句：had done主句：would/could/might/should have doneIf I had read the book,I would have told you about it.如果我读了这本书，我就会告诉你了。2、表示对现在情况的虚拟：从句：would/could/might/should do主句：动词过去式If he studied at this school，he would know the environment around the school very much.如果他在这所学校学习的话，他会很了解周边环境。3、表示对将来情况的虚拟：从句：should do/were to do主句：would/could/might/should doIf he should go to Harvard University,he would make full use of his time.如果他要上哈佛大学的话，他就会充分利用他的时间了。if的用法1、if作为连词，引导条件状语从句，表示“假如，如果”等。在复合句中如果主句用将来时，则if引导的状语从句用一般现在时。eg:If it rains(从句) ,I will stay at home（主句）。=I will stay at home if it rains.He will come if you invite him.如果你请他,他会来的。2、主句含有情态动词 （must、may、can etc.）从句为一般现在时。eg:If you drive too fast ,you may have an accident.=You may have an accident if you drive too fast.
虚拟语气if的三种用法
虚拟语气if的三种用法如下：表示与现在事实相反的情况、表示与过去事实相反的情况、表示与将来事实相反。表示与现在事实相反的情况： 1、从句：If+主语+动词一般过去时(Be动词用were)。 2、主句：主语+ should/would/might/could+do。 3、例句：If I were you，I would take an umbrella。表示与过去事实相反的情况：1、从句：If+主语+had+done。 2、主句：主语+should/would/might/could+have done。3、例句：If he had taken my advice，he would not have made such a mistake。表示与将来事实相反： 1、从句：if+主语+were to do。 2、if+主语+should+do。 3、if+主语+动词一般过去式（be动词用were）。4、例句：
