一、了解相互间关系
had better(最好),should(应该)与ought to（应该）均为提建议、阐述观点的情态动词,其后接动词原形.should 比had better语气强,ought to语气最强.一般情况下should与ought to可通用.
例1：You had better go there at once.你最好立即去那里.
例2：You ought to / should work hard.你应该努力工作.
值得注意的是：should还有"竟然"之意,表出乎意料.
例：You can't imagine that a well-behaved gentleman should be so rude to a lady.你真是难以想象这么一个有风度的先生对一个女子是如此之粗鲁.
二、 掌握句型变换方法
had better,should,ought to作为情态动词,各种句型变换均在自身形式上作变化.
（一）否定句
had better,should,ought to用于否定句时,否定词均位于其后,具体形式为：had better not do,shouldn't / should not do,oughtn't to do.
例1：You had better not start at this time.此时你最好别出发.
例2：He shouldn't be careless in class.他上课时不应粗心.
例3：She oughtn't to waste time.她不应该浪费时间.
（二）一般疑问句
had better,should,ought to用于一般疑问句时,分别将had,should,ought提至句首.
例1：Had he better start early at once?他最好立即出发吗?
例2：Should you do like this?你应该这么做吗?
例3：Ought he to go there?他应该去那里吗?
（三）反意疑问句
陈述句谓语动词含had better,should,ought to时,反意疑问句为：had,should与ought+主格人称代词或hadn't,shouldn't,oughtn't+主格人称代词.
例1：You had better not go home,had you?你最好别回家,是吗?
例2：You should study hard,
shouldn't you?你应该认真学习,是吗?
例3：He oughtn't to speak in class,ought he?你上课不应该讲话,是吗?
三、 掌握其完成式用法
had better没有完成式,should与ought to完成式意义与用法完全相同.
（一）should/ought to have done 意为本来应做但实际没有做,表达遗憾的感情色彩.
例：There was a lot of fun at yesterday's party.You ________ come,but why didn't you?
A.must have B.should C.need have D.ought to have
析：答案D.该空含你本来应来但实际未来之意,应填ought to have.
（二）should / oughtn't to have done,意为本来不应做但实际已做,表达遗憾的感情色彩.
例：I was really anxious about you.You ________ home without a word.
A.mustn't leave
B.shouldn't have left
C.couldn't have left
D.needn't leave
析：答案B.该空含你本不应该一句话不说就离开家但实际已这么做之意,所以应填shouldn't have left.
再问： 求ought to否定句的回答肯定和否定两种回答,是Yes,I ought to.还是Yes,I ought.
再答： 是Yes,I ought to
再问： 可是其他改变都只在ought上做变化?
