情态动词

can, could

1 能力 could是can的过去式. Can you skate?

2 许可 could比can 更委婉. Can I go now?

3 推测 can不能用于肯定句，但有两种情况下可以：1理论上不可能而实际有可能时 2 can加 only 时

  This can't be done by him

4 有时 can + be/get

5 惊讶，怀疑   Can this be true?

 

will, would

1 将要 would是will的过去式

 

2 提出建议或请求 would比will更委婉

Will/Would you pass me the ball,please.

3 would like 是由want 和like 变时表词而来

4 过去或现在的习惯，倾向性

 

may,might

1 允许 表请求允许时，只能用于第一人称疑问句，might比may 更委婉，表给予允许时，只能用于第二三人称陈述句中，只能用may

May/Might I smoke in this room ? No ,you mustn't

2 推测 may 不能用于疑问句句首，也就是一般疑问句，might比may的可能性要小，如果想变大加well 表示加强语气

He may/might be very busy now.

3 祝愿  may + 陈述句（动词用原型） 

May you Succeed!

4 不妨，还是 may/might + as well

 

must ,have to

1 must 表主动 ，have to 表被动.   You must come in now.    I have to go now,

2 must可以表推测，musn't 和have to 不可以

Your mother must be waiting for you now.

3 对must的否定回答用 not have to 或 not neet to

 

shall ,should,ought to ,be supposed to do

1 shall 用于第一人称疑问句中表征求意见；用于第二三人称陈述句表命令，警告，承诺，决心。

2 ought to 比 should 语气重，场合更正式

3 should = be supposed to do 表可推测

 

need dare

1 need 和 dare 有情态动词与实义动词两种用法。在疑问句与否定句中，两种都可以用；在肯定句中只能用实义动词。

 

2 need doing 可表被动