華閱文章網* 加名詞 加過去分詞
1.（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。
2. （表示虛擬）假如，要是
1）時態：可以表示過去，現在和將來的情況。它的基本特點是時態退后。
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 my lawyer had been here last Saturday, he would have prevented me fromgoing.
If he had come yesterday, I should /would have told him about it.
含義：Hedid not come yesterday, so I did nottell him about it.
If he had not been ill and missed many classes, he would have made greaterprogress.
含義：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.
3. 是否= whether 連接賓語從句
I wonder if she is ill.
* 加名詞 加過去分詞
1.（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。
2. （表示虛擬）假如，要是 1）時態：可以表示過去，現在和將來的情況。它的基本特點是時態退后。
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 my lawyer had been here last Saturday, he would have prevented me fromgoing. If he had come yesterday, I should /would have told him about it.含義：Hedid not come yesterday, so I did nottell him about * he had not been ill and missed many classes, he would have made greaterprogress.含義：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 * you should succeed, everything would be all * you were to succeed, everything would be all right.3. 是否= whether 連接賓語從句I wonder if she is ill.。
* if 后何時接動詞不定式,現在分詞,過去分詞
■as if 后面可以接不定式、現在分詞、過去分詞。但是，這種用法實際上是 ?as if 從句的省略形式。例如：
(1) He opened his mouth as if to speak.
= He opened his mouth as if he wanted to speak.
(2) He shook his head as if to say "no".
= He shook his head as if he wanted to say "no".
(3) She lifted one arm, as if to shield herself, then screamed in terror.
= She lifted one arm, as if she wanted to shield herself, then screamed in terror.
■如果 as if 從句的主語和主句的主語一致而且從句的謂語含有 be ，常常可以把從句的主語和 be 一起省略。例如：
(1) He stoodas if rooted to the ground.
= He stood as if he was rooted to the ground .
(2) He paused as if expectingLanny to speak.
= He paused as if he was expecting Lanny to speak.
* if 后何時接動詞不定式,現在分詞,過去分詞
一、as if 從句的作用 1. 在look, seem 等系動詞后引導表語從句。
如： She looks as if she were ten years younger. 她看起來好像年輕了十歲。 It seems as if our team is going to win. 看來我們隊要勝了。
2. 引導方式狀語從句。如： She loves the boy as if she were his mother. 她愛這男孩，就好像她是他的母親一樣。
The child talked to us as if he were a grown up. 那孩子跟我們談起話來，像個成年人似的。 二、as if 還可用于省略句中 如果as if 引導的從句是“主語+系動詞”結構，可省略主語和系動詞，這樣as if 后就只剩下名詞、不定式、形容詞（短語）、介詞短語或分詞。
如： He acts as if (he was) a fool. 他做事像個傻子。 Tom raised his hands as if (he was going) to say something. 湯姆舉起手好像要說什么。
She left the room hurriedly as if (she was)angry. 她匆忙離開房間好像生氣的樣子。 三、as if 從句的語氣及時態 1. as if 從句用陳述語氣的情況。
當說話者認為句子所述的是真實的或極有可能發生或存在的事實時。如： It sounds as if it is raining. 聽起來像是在下雨。
He talks as if he is drunk. 從他談話的樣子來看他是醉了。 2. as if 從句用虛擬語氣的情況。
當說話人認為句子所述的是不真實的或極少有可能發生或存在的情況時。從句虛擬語氣動詞時態的形式如下： （1）如果從句表示與現在事實相反，謂語動詞用一般過去時。
如： You look as if you didn' t care. 你看上去好像并不在乎。 He talks as if he knew where she was. 他說話的樣子，好像他知道她在哪里似的。
（2）從句表示與過去事實相反，謂語動詞用“had+過去分詞”。如： He talks about Rome as if he had been there before. 他說起羅馬來好像他以前去過羅馬似的。
The girl listened as if she had been turned to stone. 那女孩傾聽著，一動也不動，像已經變成了石頭似的。 （3）從句表示與將來事實相反，謂語動詞用“would/could/might+動詞原形”。
如： He opened his mouth as if he would say something. 他張開嘴好像要說什么。 It looks as if it might snow. 看來好像要下雪了。
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