1.动词不定式通常由不定式符号to+动词原形构成,有时可以不带to。动词不定式是动词的非谓语形式,也就是说在句子中不能作谓语,没有人称和数的变化。但动词不定式仍然具有动词的许多特点,它可以有自己的宾语和状语,和它构成不定式短语。如to see my friend, to go to school等。 2. 动词不定式具有名词、形容词和副词的 特征,因此可在句子中作主语,宾语,宾语补足语,定语和状语等。 a)动词不定式常用来做主语: To do morning exercises is good for health. 作早操对身体有意。(这里的谓语动词应用is ) 但在很多情况下,特别是在口语中,我们常用it 来代替它作主语,而把它移到句子后半部分,这样式句子显得比较平稳。 It took me one and a half hours to finish my homework. 完成家庭作业用了我一个半小时。 b)常见的作宾语的动词不定式短语有: begin to do (开始做); decide to do (决定做) forget to do (忘记做); hope to do (希望做) learn to do (学做) ; like to do (喜欢做) love to do (喜爱做); prefer to do (宁愿做) start to do (开始做); want to do (想要做) wish to do (希望做); remember to do (记得做) would like to do (想要做); try to do (努力做) agree to do (同意做)等。 c)做宾语补足语的动词不定式短语有: ask sb to do 请某人作; tell sb to do叫某人作 ; want sb to do想要某人作 ; would like sb to do想要某人作 (较前更委婉) ; prefer sb to do 宁愿某人作; like sb to do喜欢某人作; teach sb to do教某人作 ; help sb to do 帮助某人作;etc. 与make, let, see, hear, watch等词构成的短语中,动词不定时不带 to . d)动词不定式做定语修饰名词或不定代词,放在被修饰词的后面: I've a lot of homework to do . Give me something to eat . e)动词不定式常用来作状语,修饰动词,表示行为的目的,常见的短语有: come to do来作 ; go to do去做; stop to do 停下来去做etc. f)动词不定式常与连接代词或副词(由疑问代词或副词转化而来)连用,作动词的宾语,常可改为宾语从句: He asked me how to get there . =He asked me how he could get there . g)在find ,think等动词后的不定式,常用 it 代替不定式,而把不定式放到后面去: He found it difficult to get to sleep .他发现很难入睡. I think it important to learn a foreign language .我认为学习一门外语很重要. h)动词不定式的否定形式由"not +动词原形"构成: Ask him not to talk in class .请他不要在课堂上讲话.