助动词本身无意义,在句中帮助主要动词构成一定的时态,语态、语气,或是帮助构成否定句和疑问句,常用的助动词有be, do, have, shall(should), will(would).情态动词与助动词,快来和美联英语老师来收藏吧。
情态动词表一定的词义,本身并不表示动作或状态,而仅仅表达说话人的态度,它在句中须和主要动词一起构成谓语,主要的情态动词有can(could), may (might), must, have to, ought to, need, dare, shall, should, will, would.
1、can 能,可以,表说话人同意,许可还可表客观条件许可,如:you can go now.
提建议或请求时可用can i, can you表客气,如can i buy you a drink?
can和be able to表能力时的区别。
can表一般具有的能力,be able to表在特定条件下的能力,如:although the driver was badly hurt, he was able to explain what had happened.
2、may
(1)、可以,表说话人同意,许可或请求对方许可。you may go.
(2)、(现在和将来)可能,也许,只用于肯定句和否定句中,如he may not be right.
3、must, have to
must表主观上的必须,have to表客观上的必须,如:it's getting late. i have to go. -must i go now. -yes, you must.
(no, you needn't./ no, you don't have to.)
4、need, dare这二词有实意动词和情态动词两种词性,如用作实意动词后接动词不定式to do,如用作情态动词后接动词原形。need i go now? --yes, you must./no, you needn't.)
5、shall用于人称疑问句中表说话人征求对方的意见或向对方请求,如,shall we begin our lesson?
用于二、三人称陈述句,表说话人命令、警告、允诺、威胁等口吻,如: you shall fail if you don't work harder.
6、should表应该,意为有责任,有义务。如:we should try our best to make our country more beautiful.
7、will表有做某事的意志、意愿、安心、打算,如will you lend me your book? yes, i will.,
8、should have done表应该做而未做
must have done表对过去事实的肯定推测
could have done表本可以做某事
9、判断句:肯定句用must, 否定句用can't, 不太肯定用may, might