6、ought to的基本用法
(l)表示根据某种义务或必要“应当”做某事,语气比should强,例如:Everyone ought to obey the traffic regulations. (2)表示推测,注意与must表示推测时的区别:He must be home by now .(断定他已到家),He ought to be home by now .(不十分肯定),This is where the oil must be.(比较直率) ,This is where the oil ought to be. (比较含蓄) ;(3)“ought + have+ 过去分词”表示过去应做某事而 实际未做。例如:You ought to have helped him. (but you didn’t) 这时,ought与 should可以互相换用。注意,在美国英语中ought to 用于否定和疑问句时to可以省略。例如:Ought you smoke so much? You oughtn’t smoke so much.
7、dare的基本用法
(l)dare (dared为其过去式) 作情态动词用时,主要用于否定句,疑问句和条件从句中,如:Dared he bread the traffic regulations again? (2)在现代英语中dare常用作行为动词,其变化与一般行为动词相同,如:She dares to stay at home alone at night.
8、need的基本用法
(1)need作情态动词用时,主要用于否定句和疑问句中,如:He needn't worry about us now.
(2)need也可作为行为动词用,可用于肯定句,否定句和疑问句中,其后可接名词、代词、动名词或带 to 的动词不定式为其宾语。如:You need to practise reading aloud every day. (3)needn't后接完成式可以表示过去做了一件本来不必要做的事情,如:---- Did you answer the letter yesterday? ---- Yes, I did. ---- But you needn’t have answered it.
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