4.2 should, ought to, must

Form: Should, ought to, and must are modal verbs.

I should study English.
You shouldn't play tennis today.
He ought to work hard.
She ought not to watch TV today.
It must work perfectly.
We should eat less.
 

Use

1. Should and ought to express mild obligation, suggestion, or advice. They express what, in the speaker's opinion, is the right or best thing to do. We often use them with I think / I don't think ...

You're always asking me for money. I think you should spend less.
You shouldn't sit so close to the television! It's bad for your eyes.
You ought to be more careful with your money.

2. Should I / should she / should we...? is possible. We often use Do you think ...?

Should I try to eat less?
Do you think I should see a doctor?

3. Must, like have to, expresses strong obligation. Must expresses an obligation that involves the speaker's opinion. It's personal.

I must get my hair cut. (This is me talking to me.)
You must go and visit your grandmother. (A parent talking to a child.)

4. Must is also associated with a formal, written style.

All visitors must show proper ID. (Sign in the lobby of an office building.)
Books must be returned on or before the due date. (Instructions in a library.)

have to and must, don't have to and mustn't

1. Have to and must are sometimes interchangeable.

I must be home by midnight.
I have to be home by midnight.

But have to is used more often then must. If you are unsure which to use, it's probably safer to use have to.

2. Must I...? is possible, but question forms with have to are more common.

Do I have to do what you say, or can I do what I want?

3. Have to has all forms, must does not.

I had to work until midnight last night. (Past)
You'll have to study hard when you go to college. (Future)
She's a millionaire. She's never had to do any work. (Present Perfect)
I hate having to get up on cold, winter nights. (-ing form)
If you were a nurse, you would have to wear a uniform. (Infinitive)

4. Don't have to and mustn't are completely different.

Don't have to expresses absence of obligation - you can but it's not necessary.

Some people iron their socks, but you don't have to. I think it's a waste of time.
When you go into a shop, you don't have to buy something. You can just look.

Mustn't expresses negative obligation - it's very important not to do something.

You mustn't steal other people's things. It's wrong.
You mustn't drive if you've been drinking. You could kill someone!

4.3 Making requests: can, could, will, and would

1. There are many ways of making requests in English.

Can you help me, please.
Could you pass the salt, please.
Will you do this for me, please.
Would you help me, please.
Would you mind helping me, please.

Can I speak to you, please.
Could we ask you a question?
Do you mind if I open the window?
Would you mind if he opened the window?

Can, could, will, and would are all modal verbs.

2. Could is a little more formal, can is a little more familiar.

Could I ...? and Could you ...? are very useful because they can be used in many different situations.

3. Here are some ways of responding to requests.

A : Excuse me! Could you help me?
B : Sure.
   Of course.
   Well, I'm afraid I'm a little busy right now.

A : Would you mind if I opened the window?
B: No, not at all.
   No, that's fine.
   Well, I'm a little cold, actually.

4.4 Making offers : will and shall / should

1. Will and shall / should are used to express offers. They are both modal verbs.

2. The contracted form of will is used to express an intention, decision, or offer made at the moment of speaking.

Come over after work. I'll cook dinner for you.
"It's Jane's birthday today." "Is it? I'll buy her some flowers."
Give him your suitcase. He'll carry it for you.
Don't worry about catching the bus. Dave'll give you a lift.
Give it back or we'll call the police!

In many languages, this idea is often expressed by a present tense, but in English this is wrong.

I'll give you my number. NOT I give you my number.
I'll carry your suitcase. NOT I carry your suitcase.

3. Shall / Should ...? is used in questions with the first person, I and we. It expresses an offer, a suggestion, or a request for advice.

"Shall I carry your bag for you?" "That's very kind of you. Thank you."
"Shall we go out for a meal tonight?" "Mmm. I'd love to."
"What shall we do? We haven't got any money." "We could ask Dad."

We use should to make an informal suggestion.

What should we have for dinner?
What should we do tonight?