英语中,能够充当句子谓语的动词就是主动词(main verb)半助动词在功能上介于主动词和助动词之间,本身有词汇意义,可分为三类:a.以be为中心成分,如:be about to　 be going tobe bound to 　be able tobe due to　 be sure tob.以have为中心成分,如:had better/best　 have got tohave toc.以seem等为中心成分,如:seem to 　 turn out to beappear to 　 fail tohappen to 　 tend to2.半助动词既可是限定形式(体现时态,语态特征),也可是非限定形式(不定式或现在分词)。半助动词后的主动词都用带to 的不定式,这种不定式可以是一般形式、进行式或完成式,如:He appears to have many friends.他似乎有许多朋友。He seems to be enjoying himself at the party.在聚会上,他看起来很快乐。Now,I‘m having to take a bus.现在,我不得不坐公共汽车。You are supposed to have finished your term paper by Sunday evening.在周日晚上,你应该已经做完了你的学期论文省略方向为“自右而左”,也称“右省略”,可仅仅省主动词,也可连同助动词一起省略,仅剩一个作用词。(9) ?? — Yes , she might (have (been (going to (the department) ) ) )(10) —你明天会去爬山吗? —会(去) 。英语动词不定式标记to 后的动词可以省略,但在汉语相应的结构中一般不用省略。而且英语中有时可全部省去谓语动词,但汉语经常不省。(11) I will do anything you want me to.(12) 你要我做什么,我就做什么。(13) Reading maketh a full man ; conference a ready man ;?? . (F. Bacon : Of Studies)(14) 读书使人充实,讨论使人机智, (笔记使人准确) 。