1) 表请求、建议；would比will委婉

Would you like some coffee?

It is hot. Will you open the windows?

　2) 表意志、愿望和决心

I'll do my best to catch up with them.

3) will be / will have done 表推测，用于第二、三人称。前者表对目前情况的推测；后者表对已完成的动作或事态的推测。

This will be the book you want.

He will have arrived by now.

　4) used to /would的区别

　5）would表料想或猜想

It would be about ten when he left home.

I thought he would have told you all about it.

　6) will 表自然习惯，总是....

Oil will float on water.

Fish will die without water.

6. shall /should

1) shall 用于1、人称的疑问句中，征求意见。

What shall we eat this evening?

2) shall 用于2、3人称，表命令、许诺、恐吓、警告。

One day you shall be punished.

You shall have the book after I finished it.

3) should 表劝告、建议、命令，同义词是：ought to 。疑问句中常用should代替ought to.

　　You should go to bed now.

　　Should I open the door?

4) should + have done

You should have started earlier.

7. ought to

1) 用于第一人称，表有责任或有必要做某事。

We ought to be more careful with our homework.

2) 用于第二、三人称，表建议或劝告。

You ought to follow your teacher's advice.

She ought not to go alone.

3) ought to + have done: 本该...；

　　I'm sorry. I ought to have told you this morning.

8. need / dare

needn't have done

　　这两词既可做实义动词用，又可做情态动词用。作为情态动词，两者都只能用于疑问句，否定句和条件句。need 作实义动词时后面的不定式必须带to，而dare作实义动词用时, 后面的to 时常可以被省略。

9. had better表示"最好"，相当于一个助动词，它只有一种形式，它后面要跟动词原形。

had better have done sth 表示与事实相反的结果，意为"本来最好"。例如：

　You had better have come earlier. 你本该来得早一点。

　Need you go yet? 你要走了吗？

　Yes, I must. / No, I needn't.是的，我要走了/不，不急着走。

10. would rather表示"宁愿"

　 would rather do

　 would rather not do

　 would rather... than...　 宁愿...而不愿。