學習重點：Modals:must 情態動詞must
Modals: can 情態動詞can
Modals: need 情態動詞need
Modals: must 情態動詞must
我們已經嘗過了表示義務的must和have to。在現在時里面可能使用must和have to，但在其他時態里只能have to。
Postive Obligation 表示肯定意思的和義務（時態）
現在 主語+must+動詞*
主語＋have to +動詞
主語+have got to +動詞
將來 主語+will+have to +動詞
主語+be going to =have to +動詞
We will have to see
He is going to have to drive
過去 主語+had to +動詞
You had to resign.
現在完成 主語+have tp +動詞
I have had to stop
She has had to sing.
Negative Obligation 表示否定意思的責任和義務
表示否定的義務，即禁止時，在現在時里可以用must,而在其他時態里則必須用be forbidden to 或not be allowed等。
現在 主語+must not(mustn’t )+動詞
You mustn’t leave.
將來 主語+will be forbidden to+動詞
主語+be going to be forbidden to +動詞
主語+will not be allowed to +動詞
主語+be not going to be allowed to +動詞
You will be forbidden to leve.
You are going to be forbidden to leave.
He will not be allowed to eat.
He’s not going to be allowed to eat.
過去 主語+was/were forbidden to +動詞
主語+was /were not allowed+動詞
I was forbidden to speak
We were not allowed to see.
現在完成 主語+have been forbidden to+動詞
主語+have not been allowed to +動詞
He has beren forbidden to move.
They have not been allowed to talk.
No Obligation不做……也行
現在 主語+do not have to +動詞
主語+have not got to +動詞
I don’t have to go.
She hasn’t got to look.
將來 主語+will not（won’t)+have to +動詞
主語+be not going to =have to +動詞
I won’t have to lie.
We aren’t going to have to move.
過去 主語+did not have to+動詞
She didn’t have to dance.
現在完成 主語+have not had to +動詞
I haven’t had to work.
*此處指動詞原型，也就是不加to的不定式。
Modals: can 情態動can
Expressing permission表示許可
現在時里可以用can, 過去時和條件時態里要用could,而其他時態里必須用be allowed to ,be permitted to 等表達。
現在：主語+can+動詞
主語+be+allowed/permitted +to+動詞
I can go .
She’s allowed/permitted to leave.
過去：主語+could動詞
主語+was/were +allowed/permitted +to +動詞
We could see.
It was permitted/allowed to continue.
將來：主語+will be allowed to +動詞
主語+be+going to be allowed/permitted to +動詞
I will be allowed/permitted to travel.
We are going to be permitted/allowed to attend.
條件：主語+could+動詞
主語+would be +allowed/permitted +to +動詞
He could do it.
We would be allowed/permitted to visit.
Expressing Ability 表示能力
現在時態里可以用can,過去時態和條件時態里要用could, 而其他時態里必須用be able to.
現在：主語+can +動詞
主語+be able to +動詞
I can dance.
We are able to sing.
過去：主語+could +動詞
主語+was/were+able to+動詞
You could draw.
They were able to choose.
將來：主語+will be able to +動詞
主語+be going to be able to+動詞
We will be able to fly.
She is going able to travel.
條件；主語+could+動詞
主語+would be able to +動詞]
They could drive.
He would be able to work.
Expressing possibility 表示可能性
在現在時態里用can,過去時里用could。
The weather can be very cold at this time fo year.每年這個時候都很冷。In the old days, the people of bognor could be very aggressive. 在古代，伯格諾人是非常好斗的。
Modals:need 情態動詞need
Need后面加不定式，可以變成表示“有必要”的情態動詞“。
在現時態里，它和一般動詞一樣，接在單數第三人稱后面，要加-s;在否定句、疑問句里要用do/does.
*19\20單元里，為了方便起見，我們把意思上類似情態動詞的表達（have need to ）稱作情態動詞。
●肯定句 I need to see you.我應該去見你。
He needs to see you.他應該去你。
●疑問句 Do you need to come? 你一定要來嗎？
Does he need to come?他一定要來嗎？
●否定句：You don’t need to come.你不一定要來。
He doesn’t need to come. 他不一定要來。
或者： You needn’t come.
He needn’t come.
即使在單數第三人稱后，needn’t 也不參加-s,而且它后面接的是不加to的不定式。
它的過去時和將來時的方法和一般動詞一樣。
They needed to talk to you.
Did rhey need to talk to you?
They didn’t need to talk to you.
They will need to talk to you.
They are going to need to talk to you.
Will they need to talk to you?
Are they going to need to talk to you?
They won’t need to talk to you.
They ‘re not going to need to talk to you.
英國英語里還有needn’t have 這種過[的表達方法，表示的是“雖然沒必要做，但還是做了”。
You needn’t have told him the truth.你不應該告訴他實情。
