if的用法总结
if的用法:表示条件,意思是如果;表示虚拟,意思是假如;表示是否的含义,和whether相同用法,连接宾语从句。
1.(表示条件)如果 ,主句用将来时,if从句用现在时表示将来
He will come if you invite him.
如果你请他,他会来的.
2.(表示虚拟)假如,要是
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) h***e+ 过去分词
If she had worked harder,she would h***e succeeded.
The rice would not h***e been burnt if you had been more careful.
If my lawyer had been here last Saturday,he would h***e prevented me from going.
If he had come yesterday,I should / would h***e 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 h***e 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.
3.是否 = whether 连接宾语从句
I wonder if she is ill.
不知她是否病了.