had better, should, ought to学习四要素（一）
had better，should，ought to 均为提建议型情态动词，常用来劝告别人去做某事，没有人称和数的变化，学习时应注意下列几点：
一、掌握基本用法
had better，should，ought to 含义及语气有所不同，请看下表：
二 、掌握创新用法
should 可表竟然，强调惊讶的情绪。
I cant imagine this problem should be so easy.
我想像不出这个问题竟然这么容易。
had better 也可改为 had best ，其意义和用法不变。
Im busy now，so you had best go there alone.
我现在很忙，所以你最好单独去那儿。
三、掌握句型变换方法
had better，should，ought to 均属于助动词，其疑问句、否定句及反意疑问句的构成均在自身形式上做变化。
1. 变成否定句方法
had better do 否定式为 had better not do，should do 否定式为 should not do 或 shouldnt do，ought to do 否定式为 ought not to do 或 oughtnt to do .
2. 变成一般疑问句方法
had better，should，ought to 构成一般疑问句时应分别将 had，should，ought 提到句首，其肯定与否定回答为 had / hadnt，should / shouldnt，ought / oughtnt .
3. 变成反意疑问句方法
had better，should，ought to 构成反意疑问句时通常使用 had / hadnt，should / shouldnt，ought / oughtnt 形式。
She had better water the flowers as soon as possible，hadnt she？
她最好尽快给花浇水，不是吗？
All of us should take an active part in this activity，shouldnt we？
我们都应该积极参加这次活动，不是吗？
They oughtnt to go fishing in this river，ought / should they？
他们不该在这条河里钓鱼，是吗？
四、掌握完成式用法
should 与 ought to 完成式意义和用法相同，可以通用。should / ought to have done sth. 本来应该做某事但实际未做，表达一种遗憾的感情色彩。shouldnt / oughtnt to have done sth. 本来不应该做某事但实际已做了，也表达一种遗憾的感情色彩。 had better 没有完成式。
The meeting has already begun. You should have come here half an hour ago.
会议已经开始了，你本来应该半小时之前就到这儿。
She is very sad now. You oughtnt to have told her the news.
她现在很难过，你本不该把这消息告诉她。[1][2]