英語語法解析：情態(tài)動(dòng)詞

情態(tài)動(dòng)詞的使用：can, must, may, might, need,
1.情態(tài)動(dòng)詞can(能夠), must(必須), may(可以)
結(jié)構(gòu)：主語+can/must/may+動(dòng)詞原型
He can make the tea.
Sally can air the room.
We can speak English.
變疑問句將情態(tài)動(dòng)詞移到句首
Can he make the tea?
Can Sally air the room?
Can we speak English?
變否定句在情態(tài)動(dòng)詞后面加not
He cannot make the tea.
Sally cannot air the room.
We cannot speak English.
肯定回答及否定回答
Yes, he can. No, he cannot.
Yes, she can. No, she cannot.
Yes, we can. No, we cannot.
特殊疑問句：
What can you do?
注意：情態(tài)動(dòng)詞的句子沒有第三人稱單數(shù)的變化，不要在情態(tài)動(dòng)詞或動(dòng)詞后面加S。
2.Must/have to的區(qū)別
must 表示必須，是主觀上覺得應(yīng)該做，have to是不得不，是由于客觀條件逼迫的必要要做
must 只能用在表示現(xiàn)在和將來的句子里，而have to do可以用在任何時(shí)態(tài)
3.must, may, might表示猜測：
must do 表示對(duì)現(xiàn)在事實(shí)的猜測
must have done表示對(duì)過去事實(shí)的猜測
must have been doing 表示對(duì)過去正在進(jìn)行的事實(shí)的猜測
may/might do, may/might have done表示沒有任何事實(shí)依據(jù)的猜測，might的可能性更小。
can’t/couldn’t 表示不可能
4.need 用法：
表示“需要”時(shí)為實(shí)意動(dòng)詞，后面可以加名詞，也可以加不定式：
I need a pen. Do you need any beer? No, I don’t.
I need to have a rest.
Need doing=need to be done，表示被動(dòng)
The flowers need watering.
Need在否定時(shí)做情態(tài)動(dòng)詞使用
You needn’t go so early. =You don’t need to go so early.
Must I clean the desk right now? No, you needn’t.