CAN/COULD.

CAN/COULD.

1. ABILITY.

a. Present and future.

CAN is usually used to talk about the present or the general ability, -the ability to do
something any time you want to.
Look! I can do it!
You can certainly cook even if you can't do anything else.
BE ABLE is also possible but less common.
I'll be able to speak Spanish in a few months.
But CAN is often possible when people make present decisions about future ability.
We're too busy today, but we can repair your car tomorrow.
Can you come to a party on Saturday?

b. Past.

COULD is used for "general ability", to say that you could do something any time you wanted to.
She could sing like an angel when she was a kid.(or she was able)
My father could speak six languages.
COULD is not used to talk about particular ability (to do something on one occasion) in the past.
Instead we use WAS ABLE TO DO, MANAGED TO DO or SUCCEEDED IN DOING.
How many eggs was he able to eat in the competition? (not could)
He managed to eat 80 eggs . (not could)
After six hours' climbing, we succeeded in reaching the top of the mountain. (not could)
The negative COULDN'T is used for both general and particular ability.
When I was younger, I couldn't decide what I wanted to do.
Salim was so tired that he couldn't reach the front door.

c. Conditional COULD.

COULD is also used in a conditional sense (meaning "would be able to).
I could have a really good time if I had a flat of my own.
We could do it by midday if we had the tools.

d. Could with the perfect infinitive.

Sometimes we want to say that we had the ability to do something, but we didn't try to do
it. There is a special structure for this: COULD + perfect infinitive.
I could have married anybody I wanted to
I could have bought it!
You could have helped me!
The structure can have a conditional meaning:
He could have won if he hadn't fallen down during the race.
Negative sentences with this structure express the idea of "I wouldn't have been able to do it even if I had tried".
I couldn't have won, so I didn't go in for the race.

2. POSSIBILITY (CAN and COULD, MAY and MIGHT)

a. Theoretical possibility.

CAN is used to say that events and situations are possible (without talking about the
chances of them actually happening).
Anybody who wants to can become a volunteer in our community.
How many books can fit into this school bag?
Sentences with CAN often give information about the characteristic behaviour of people or things.
Agadir can be very warm in December.
Gold can't be dissolved in hydrochloric acid.
To talk about the past, COULD is used.
My grandmother could be very unpleasant at times.
We often use CAN to make suggestions about possible solutions to a problem, or possible actions.
We've got three choices: we can go to the police, we can talk to him ourselves, or we can forget all about it.
In order to make suggestions more "tentative" -less strong and definite- we use COULD.
We could try asking Leila, if you think it's a good idea.
Could we meet again tomorrow?

b. Chances.

1. Future possibility.

We don't use CAN to say that there is a chance that something will happen.
Instead, we usually use MAY or MIGHT.
We may go climbing this summer.
COULD is used to give the idea that something is just possible, but not particularly likely.
We could go climbing this summer, but I doubt if we'll have time.

2. Present possibility.

MAY, MIGHT and COULD are also used to say that something is possibly true at the moment of speaking.
You may be right.
You could be right, but I don't think you are.
This could be your big chance.
CAN is sometimes used to talk about present possibility, but only in questions and negative
sentences.
Who can that be at the door?
Can it be Sara? (Not *It can be Susan)
What can she possibly want?
It can't be true. (not *It can be true)

3. CAN and COULD with the perfect infinitive.

CAN and COULD are both used with the perfect infinitive (have + past participle) for speculating or guessing about the past. CAN is only used in questions and negative sentences.
Where can he have gone?
He can't have gone to school. It's Saturday.
He could have gone off with some friends. (not can)
COULD with the perfect infinitive, is also used to talk about an unrealized past possibility:
something that was possible but didn't happen.
You were stupid to go cycling there. You could have broken your leg.
It wasn't a good idea to throw the bottle out of the window. It could have hit somebody.
You could have told me you had invited people to dinner (used to criticize people)
My parents wanted me to be a doctor, but I couldn't have put up with all those years of
study. (something was not possible.)
MAY and MIGHT can also be used with the perfect infinitive in similar ways to COULD.

3. PERMISSION (CAN and COULD, MAY and MIGHT)

a. Asking for permission.

CAN, COULD, MAY and MIGHT are all used in asking for permission. CAN is probably
the commonest of the four.
Can I have more tea , please?
COULD is rather more hesitant than CAN, and is used when you are not sure that you will get a permission (or when you don't want to sound too sure).
Could I ask you something if you are not too busy?
MAY and MIGHT are used in a more formal style. MIGHT is more hesitant and is not very
common.

b. Giving permission.

When we give permission we use CAN and MAY but not COULD or MIGHT.
Could I use your phone? Yes, of course, you can. (not could)
Might I trouble you for a light? You may indeed. (not might)

4. OFFERS AND REQUESTS.

CAN and COULD are often used to offer to do things for people, and to ask other people
to do things. COULD is more hesitant, less definite than CAN and it is used when we want to make an offer or a request seem more polite or respectful. Statements and questions are both common.
I can lend you two hundred dirhams till Wednesday if that will help.
I could do the shopping for you, if you're tired.
Can I carry your bag?
Could I give you dinner one of these days?
You can start by doing the washing up, and then you can clean the car.
You could phone Aicha and see what time she's coming.
Can you come here a minute, please?
Could you help me with this exercise, please?