English English Grammar Grammar

in Usein Use

could (do) & could have (done) ;

must & can’t ; might as well

needn't do & needn't have done;

should; can & could;

if I do & if I did; I wish I did;

I wish ...would

情景语法 3 ：情态动词

• A: What shall we do this evening?

• B: We could go to the cinema.

Sometimes “could” is the past of “can”. Sometimes “could” is used in the future (especially to make a suggestion)

could (do) & could have (done)

Compare

could (do) could have done

I'm so tired. I could sleep for a week. (now)

I was so tired. I could have slept for a week. (past)

Why did you stay at a hotel when to New York? You could have stayed with Barbara.

Jack fell off a ladder yesterday but he's all right. He's lucky - he could have hurt himself badly.

but he didn't hurt himself

you had opportunity to stay with her but you didn't

Most often, we use could have (done) for things which were possible but did not happen:could have done

must & can’t

• My house is very near the motorway.• It must be very noisy.

You've been traveling all day. You must be tired.

'Jim is a hard worker.' 'Jim? A hard worker? You must be joking. He's very lazy.'

Traveling is tiring and you've been traveling all day, so you must be tired.)

mustWe use “must” to say that we feel sure something is true:

Carol must get very bored in her job. She does the same thing every day.

You've just had lunch. You can't be hungry already.

Brian said he would definitely be here before 9.30. It's 10 o'clock now and he's never late. He can't be coming.

(People are not normally hungry just after eating a

meal. You've just eaten, so you can't be hungry.)

We use “can't” to say that we feel sure something is not possible:

They haven't lived here for very long. They can't know many people.

Can’t

might as well

Helen: What shall we do? Shall we walk?

Clare: We might as well. It's a nice day and I don't want to wait here for an hour.

(Helen and Clare have just missed the bus. The buses run every hour.)

A: What time are you going? B: Well, I'm ready, so I might as well go

now.

or ... I may as well go now

'(We) might as well do something'= (We) should do something because there is nothing better to do and there is no reason not to do it. You can also say 'may as well'.

The buses are so expensive these days, you might as

well get a taxi.

might as well

= taxis are just as good,

no more expensive

Compare

must do mustn't do

You must do something' = it is necessary that you do it

You mustn't do something' = it is necessary that you do not do it (so don't do it)

Compare

must do mustn't do

Don't tell anybody what I said. You must keep it a secret.

We haven't got much time. We must hurry.

You must keep it a secret. You mustn't tell anybody else.

It's essential that nobody hears us. We mustn't make any noise.

(= don't tell anybody else)

needn't do & needn't have done

• I think it's going to rain. I'll take the umbrella.

(George had to go out. He thought it was going to rain, so he decided to take the umbrella.)

• I needn't have brought the umbrella.

(But it didn't rain, so the umbrella was not necessary. )

needn't do & needn't have done

That shirt isn't dirty. You needn't wash it. Why did you

wash that shirt? It wasn't dirty. You needn't have washed it.

Compare

needn't do needn't have done

Compare

didn’t needn't do needn't have done

I didn't need to ... = it was not necessary for me to... (and I knew this at the time):

'I needn't have (done) something' = I did something but now I know that it was not necessary

I didn't need to get up early, so I didn't.

I didn't need to get up early, but it was a lovely morning, so I did.

I got up very early because I had to get ready to go away. But in fact it didn't take me long to get ready. So, I needn't have got up so early. I could have stayed in bed longer.

Compare

didn’t needn't do needn't have done

should

He should be wearing a helmet.

(= she isn't here yet, and

this is not normal

We use should when something is not right or what we expect. For example:should

I wonder where Liz is. She should be here by now.

The price on this packet is wrong. It should be L1.20, not L1.50.

Those boys shouldn't be playing football at this time. They should be at school.

can & could

Could you open the door, please?

We often use can or could to ask people to do things:can & could

Liz, can you do me a favor?

Can you wait a moment, please?

Could you wait a moment, please?

Excuse me, could you tell me how to get to the airport?

I wonder if you could help me.

If I do & if I did

If I won a million pounds…

Sue has lost her watch. She thinks it may be at Ann's house. Ann feels there is a real possibility that she will find the watch.

If I do

SUE: I think I left my watch at your house. Have you seen it?

ANN: No, but I'll have a look when I get home. If I find it, I'll tell you.

Here, Ann is not thinking about a real possibility; she is imagining the situation and doesn't expect to find a wallet in the street.

if I did

Ann says: If I found a wallet in the street, I'd take it to the police.

If I did & I wish I did

If I knew his number.

She is imagining the situation. The real situation is that she doesn't know his number.

I wish I had an umbrella.

If I did & I wish I did

We use “wish” to say that we regret something, that something is not as we would like it to be.

I wish ...would

I wish it would stop raining.

Jill is complaining about the rain and wants it to stop.

We use I wish ... would... when we want something to happen or when we want somebody to do something. The speaker is not happy with the present situation.

I wish ...would

The phone has been ringing for five minutes. I wish somebody would answer it.

I wish you would do something instead of just sitting and doing nothing.