在语法中，动词不定式是指动词的一种不带词形变化从而不指示人称、数量、时态的形式。它之所以被叫做不定式，是因为动词不被限定，或者说不被词形变化所局限。不定式属于非谓语动词。
动词后接另一个动词作宾语
1、英语中有些动词后接另一个动词作宾语时，用作宾语的动词习惯要用不定式，而不用动名词，这类动词主要有：afford(负担得起), agree(同意), apply(申请), arrange(安排), ask(要求), care(想要), choose(决定), decide(决定), demand(要求), determine(决心), expect(期待), help(帮助), hope(希望), manage(设法), offer(主动提出), plan(计划), prepare(准备), pretend(假装), promise(答应), refuse(拒绝), want(想要), wish(希望)等。
2、如：Less and less people can afford to go abroad for their holidays. 花得起钱去国外度假的人越来越少了。He agreed to help but backed out when he found how difficult it was. 他本来同意给予帮助的，但在发现事情有多么困难之后就打退堂鼓了。Bill applied to join the police last week, but he wasn’t tall enough. 比尔上星期申请参加警察部队，但是他不够高。We arranged to meet at the station but she didn’t turn up. 我们商量好在车站见面，可是她没有露面。There have been fewer problems for travelers who chose to fly. 对于选择乘飞机旅游的人来说问题更少。He decided to put an advertisement in the newspapers. 他决定在报上登一份广告。He was very ill for a time, but he managed to pull through. 有一段时间他病得很重，但他最后痊愈了。She pretended to be angry, but she was not. 她假装生气，却并未生气。
