真实和非真实条件句各表示什么含义?分别怎么用?又有什么区别和联系?

真实和非真实条件句各表示什么含义?分别怎么用?又有什么区别和联系?

真实条件句
真实条件句用于陈述语气,假设的情况可能发生,其中 if 是如果的意思.
　　时态关系
句型：条件从句　　　 主句
一般现在时　　 shall/will + 动词原形
　If he comes,he will bring his violin.
典型例题
　The volleyball match will be put off if it ___.
A.will rain　 B.rains　 C.rained　 D.is rained
　答案B.真实条件句主句为将来时,从句用一般现在时.
非真实（虚拟）条件句
1）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.表示与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.