什么时候用动名词什么时候用不定式？

非谓语动词包括动词不定式。动名词和分词三种形式,分词又包括现在分词和过去分词。这三种形式都是由动词变来的,但在句子中都不能作谓语,故这三种形式被称为非谓语动词。下面就这三种形式在用法上的区别浅析如下: 　　一、动词不定式和动名词在句子中均可作主语和表语　　在表示一个具体的。个别的或将来的动作时,要用动词不定式。如: 　　My job is to teach the first-year students grammar. 　　To study English well is very important. 　　在表示比较抽象的一般的行为和动作时,二者可以互换。如: 　　To climb mountains is a good form of exercise. 　　Climbing mountains is a good form of exercise. 　　二、动名词、现在分词和动词不定式都可以作定语　　1.动名词作定语时,和它所修饰的名词之间没有逻辑上的主谓关系,只表示被修饰名词的一般用途,必须位于名词之前。如: 　　There is a swimming pool in our school. 　　2.现在分词作定语时,和它所修饰的名词之间有逻辑上的主谓关系,表示所修饰名词的特征。如: 　　Listen to the singing bird. 　　Who is the boy running towards us。　　3.动词不定式作定语时,当所修饰的名词指人时,和它所修饰的名词之间有逻辑上的主谓关系。如: 　　He is always the first to come to school. 　　当所修饰的名词指物时,和它所修饰的名词之间有逻辑上的动宾关系。如: 　　I have a meeting to attend. 　　如果作定语的动词不定式中的动词是不及物动词,需加上相应的介词。如: 　　I have no room to live in. 　　There is nothing for me to worry about. 　　三、动词不定式和分词均可作宾语补足语　　动词不定式作宾语补足语时,表示动作已经发生,动作的全过程已经结束。如: 　　I heard him knock at the door three times.(=I heard he knocked at the door three times (动作的全过程已经结束) 　　现在分词作宾语补足语时,表示动作正在进行。如: 　　I heard him knocking at the door.(= I heard he was knocking at the door.(动作正在进行) 　　过去分词也可以作宾语补足语。如: 　　I found the glass broken.(= I found the glass was broken.) 　　注意:动词不定式作宾语补足语时,在动词make,let,have,see,notice,hear,watch, observe,feel,listen to等后面要省略不定式符号to。如: 　　I hear him play. 　　The teacher made him do the exercises again. 　　help后的动词不定式作宾语补足语时,不定式符号to可加可不加。如: 　　He often helps me to study English in his spare time. 　　当这些动词变为被动语态时,原不定式必须加上to。如: 　　He was seen to repair the machine. 　　四、动词不定式和动名词均可作宾语　　1.下列动词后只能跟不定式作宾语: hope, agree, decide, manage, wish, refuse, dare, promise等。如: 　　He has promised to lend me the dictionary. 　　2.下列动词后只能跟动名词作宾语: enjoy, finish, avoid, practise, mind, escape, excuse, suggest, consider(考虑), give up, can't help等。如: 　　He wants to give up smoking. 　　They practise speaking English every day. 　　3.在动词remember,forget,regret,stop,try等后面跟动词不定式或动名词时,意义上有所差别。如: 　　He forgot telling me the news.他忘了曾经告诉过我这个消息。　　He forgot to tell me the news.他忘了要把这个消息告诉我。　　五、动词不定式和分词均可作状语　　不定式作状语通常表示"目的"或"程度";分词作状语通常表示"伴随情况"。"时间"或"原因"等。如: 　　He went to the library to borrow a book (表目的) 　　The boy sat at the desk reading a book.(表伴随情况) 　　六、动词不定式和动名词均有复合结构　　不定式的复合结构:for sb.(not) to do sth. 　　动名词的复合结构:名词所有格或形容词性物主代词+动名词。如: 　　It's important for us to learn English well. 　　He prided himself upon his dancing.

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