词形无变化 词形有变化 need 既可以是情态动词,也可以是实义动词,具有双重性。 〔四〕情态动词的根本用法 1. can (could) 1〕表示会做某事,有能力做某事。意思 = be able to 其否认式 can’ t 用 could 和 couldn ’ t. 〔即有种能力,尤其是生来具备的能力,此时 may 和 He can speak English, but he can ’ t speak Japanese. = He is able to speak English, but he isn ’ t able to speak Japanese. I could smile but I couldn ’ t speak when I was 2 months old. = I was able to smile but I wan s’ t able to speak when I was 2 months old. 区别: 1、 can 只用于现在时和过去时 (could), be able to 可用于各种时态。 They will be able to tell you the news soon. 2、 be able to 不与 can 连用,但可以和其他情态动词或助动词连用。 He may be able to speak English very well some day in the future. 3 、用在过去时中, could 经常表示能够做某事,事实上不一定去做,而
表示“不能〞 。在过去时中 must 均不可代替它〕 。 was∕were able to 那么表示 “过去做成了某事〞。在否认句中两者可通用。 2〕用于征求意见 —— Can /Could /May /Might I(we) do sth? —— Yes, you can/may. / Of course you can. —— No(Sorry), you can ’ t. /mustn ’t. 注意:①此处的 could 和 might 都不表示过去,只是语气上的委婉,不用作答复。 ②否认答复中,表示对他人造成一定伤害或影响,或表示违反了某种规定或法律时,用 mustn’ t 较好。 . —— Could I take the book out of the library? —— May I smoke here? —— I ’ m afraid you mustn ③表示过去能力时, could 提问,只能用 could 答复。 . —— Could you ride a bike when you were 4 years old?
—— ’ t.
Sorry, you mustn ’ t. —— No, I couldn
’t. 3〕表提出意见或请求 Can/Could you (please) do sth? = Would you (please) do sth?
〔此句型中
some
不变
any〕 . Could you please give me a hand? Would you please pass me some salt? 4〕表示允许或承诺 =may . OK. You can /may come and find me at any time tom