if的用法总结 (英语)

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.

.(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) 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 .

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.

3. = whether 连接宾语从句

I wonder if she is ill.

不知她是否病了.

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