动词不定式作主语 动词不定式的基本形式为“to + 动词原形”,其否定形式是“not to +动词原形”。它能起名词的作用,在句子中充当主语、表语、宾语和宾语补足语。动词不定式在作主语时,用法主要有以下两种: 一、动词不定式作主语时常用it作形式主语,而往往将动词不定式放在谓语或表语之后。如: It's not easy to learn a foreign language well. (=To learn a foreign language well is not easy.) 学好一门外语不容易。 在此句型中,如果要说明动词不定式的动作是谁做的,可在不定式前加一个for 引起的短语,作不定式的逻辑主语。如: It's difficult for us to finish the work. 对我们来说,完成这项工作很困难。 It's hard for me to answer your question. 要我回答你的问题很难。 但是,如果表语是kind, nice, right, wrong, clever, polite 等描述行为者的性格、品质的形容词,则应在不定式前加一个of 引起的短语。如: 这个例子属于上面的换一个of引起的。 It's very kind of you to help me.你能帮我,真好。 注意: 1. of sb.和for sb.这两种结构还有一个区别,在of sb.结构中,可用sb.直接作句子的主语来改写成“It's+形容词+of sb.+动词不定式”结构。试比较: It's foolish of him to go alone. (=He was foolish to go alone.) 他单独出去太傻了。 It's kind of you to give me the book. (=You are kind to give me the book.) 你给我这本书,真是太好了。 for sb.结构则不能这样转换。例如,不可以说:We are difficult to finish the work. 2. 动词不定式作主语,同时有另一个不定式作表语时,不能转换成“It's...to do sth.”的句型。如: [正] To see is to believe. 百闻不如一见。 [误] It's to believe to see. 二、“疑问代(副)词+动词不定式”也可以在句中作主语。如: How to control the water pollution is a big problem. 如何控制水污染是一个大问题。 When to start the project remains undecided. 什么时候开始这项工程仍然没有决定。
动词不定时与动名词区别与联系 Ⅰ.动名词和不定式做主语的相同点 1.不定式短语和动名词做主语时,常常为了保持句子的平衡,用it来做形式主语,如: It is not easy to learn English well. It is no use asking him for help. 2.如果主语用了不定式,表语和宾语也要用不定式;主语用了动名词,表语和宾语也要用动名词,这在英语中称为对称性,如: To see is to believe. = Seeing is believing. (眼见为实) (85)It is better to stay home than _A__ out. A. to go B. going C. go D. gone Ⅱ.动名词和不定式做主语的不同点 1.不定式做主语常表示具体的某一动作;表示泛指或一般的抽象的概念时,多用动名词,如: (92)_B_ is a good form of exercise for both young and old. A. The walk B. Walking C. To walk D. Walk 2.在”There/It +be+ no use(good/help/need)”之后常用动名词做主语,而少用不定式,如: It /There is no use crying over the split milk. It /There is no help taking this medicine. ★但是如果该句型中用了for引出不定式的逻辑主语,就只能用不定式,如: (93) There is no good for us to do that exercise. 3.不定式可以和when, where, how, what, whether等连用,在句子中做主语,宾语和表语,而动名词则不能,如: How to solve the problem is a hot potato. Where to put the box seems hard to decide. Whether to do it hasn’t been decided. What to do next is up to you.