4)表示猜测、推测must常用于肯定句中表示猜测。对现在或未来的事进行猜测时，后接动词原形;对已经发生的事进行猜测时，后接have 过去分词。例如：

　　You must be tired after working so long .你工作这么久以后，肯定累了吧。

　　It must be that naughty boy crying outside .肯定是那个调皮的孩子在外面大叫。

　　The idea must be accepted by the society sooner or later.

　　这种想法肯定或迟或早会被社会所接受的。

　　It must have rained last night for it is so wet outside .

　　外面这么湿，昨晚肯定下雨了。

　　I didn't see you in class yesterday. You must have been

　　absent .我昨天上课没见着你，你肯定没有来。

　　Ought (后接带to的不定式构成谓语动词)应该

　　Ought (后接带to的不定式构成谓语动词)应该

　　1)表示出于职责、义务该做某事

　　You ought not to be so careless in your work .你不应该在工作上如此粗心大意。

　　We ought to study hard for the sake of our motherland.

　　我们应该为了我们的祖国而努力学习。

　　His doctor said to him that he oughtn't to smoke so much .

　　他的大夫说他不应该抽这么多烟。

　　Oughtn't you to give us a chance to try ?

　　你难道不应该给我们一个尝试的机会吗?

　　2) 表示极有可能发生某事

　　As an auto repairman ， Dick ought to know what is wrong with the car .

　　狄克作为一个汽车修理工总该知道这部车的毛病所在吧。

　　If we set off right now ， we ought to be able to get there in time .

　　如果我们马上出发，我们应当能够按时到达那里。

　　Tomorrow ought to be a nice day for we have such a fine sunset today .

　　今天有这么好的晚霞，明天准是个晴天。

　　need(用于否定句和疑问句)需要

　　There are still one and a half hours to go ， we needn't be insuch a hurry .

　　还有一个半小时，我们无需如此慌慌张张。

　　I hardly need say how much we missed you .不用说我们是多么想念你啊。

　　Need you go so soon ?你需要这么早就去吗?

　　You need have no anxiety on my account .你不必为我而着急。

　　dare ， dared(用于否定句、疑问句和疑问句)敢

　　Dare you stay here alone in the night ? 你敢在夜里呆在这儿吗?

　　Nobody dared mention that matter. 没有人敢提那件事。

　　How dared you say that to her ? 你怎么敢对她说那件事?

　　Even if you dare do it ， I won't allow you to because it's too dangerous .

　　即使你敢做，我也会让你做那件事，因为太危险了。