不定式作表语

　　1. 一种情况为主语是不定式(表示条件)，表语也是不定式(表示结果)

　　To see is to believe/ To work means to earn a living.

　　2. 另一种情况主语是以aim， duty， hope， idea， happiness， job， plan， problem， purpose， thing， wish等为中心的名词，或以what引导的名词性从句，不定式表语对主语起补充说明作用

　　His wish is to buy a luxurious car in the near future. / The boss's plan is to start building the skycraper immediately. / What I want to say is to get rid of the plan forever.