在大学英语四六级中，单独考察的题几乎没有，但是语法知识点却贯穿整张试卷，下面是小编为大家整理的知识，希望可以为大家带来帮助，一起来学习一下吧。
　　非真实条件句
　　时态：可以表示过去，现在和将来的情况。它的基本特点是时态退后。
　　a. 同现在事实相反的假设。
　　句型 ： 条件从句
　　主句
　　一般过去时
　　should( would) 动词原形
　　If they were here, they would help you.
　　b. 表示于过去事实相反的假设。
　　句型： 条件从句
　　 主句
　　过去完成时
　　should(would) have 过去分词
　　If she had worked harder, she would have succeeded.
　　The rice would not have been burnt if you had been more careful.
　　If my lawyer had been here last Saturday, he would have prevented me from going.
　　If he had come yesterday, I should / would have told him about it.
　　含义：He did not come yesterday, so I did not tell him about it.
　　If he had not been ill and missed many classes, he would have made greater progress.
　　含义： He was ill and missed many lessons, so he did not make greater progress.
　　c. 表示对将来的假想
　　句型：条件从句
　　 主句
　　一般过去时
　　 should 动词原形
　　were 不定式
　　 would 动词原形
　　should 动词原形
　　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.