if的用法

發(fā)布時間：2025-08-23 | 來源：互聯(lián)網轉載和整理

if作為從屬連詞，可引導條件狀語從句、讓步狀語從句和名詞從句。另外，if還能用作名詞，表示不確定的情況。

用法一、（表示條件）如果，主句用將來時，if從句用現在時表示將來

He will come if you invite him.

如果你請他，他會來的。

用法二、（表示虛擬）假如，要是

時態(tài)：可以表示過去，現在和將來的情況。它的基本特點是時態(tài)退后。

a、同現在事實相反的假設

句型：條件從句 主句

一般過去時 should(would)+動詞原形

If they were here,they would help you.

b、表示于過去事實相反的假設

句型：條件從句 主句

過去完成時 should(would) have+ 過去分詞

If she had worked harder,she would have succeeded.

The rice would not have been burnt if you had been more careful.

If he had come yesterday,I should / would have told him about it.=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.=He was ill and missed many lessons,so he did not make greater progress.

c、表示對將來的假想

句型：條件從句、主句

一般過去時 should+動詞原形

were+不定式 would+動詞原形

should+動詞原形

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.

用法三、表示是否，等同于whether，連接賓語從句

I wonder if she is ill.

不知她是否病了。