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Can - Could

English Grammar - Modal Verbs

Both Can and Could are Modal Verbs. In general Could is considered more polite (or formal) that Can.

CAN

The three main uses of Can are: 1) ability 2) possibility and 3) permission. However there are some other used of Can as we will see below.

1. To express ability

Can means to be (physically) able to do something OR to know how to do something.

Birds can fly.

Elephants can't fly.

I can speak two languages.

You can drive as fast as you want on the German motorways.

2. To express a possibility (in general)

This refers to a theoretical possibility.

Note: we don't use can to talk about future possibilities. For this you would use may or might.

It can get cold there at night so take a jacket.

I know you can win the competition.

Well, I think your car can be repaired, but it's not going to be cheap.

3. To offer to do something for others

Can is used when you offer to help someone or to do something for them.

You don't need to walk home. I can take you there if you like.

Can I carry your bags for you?

4. To ask for or give permission / To request something

Can is used to ask for / request permission or to give permission.

Note: Can't is used to refuse permission.

You can use my umbrella, I don't need it right now.

Can I sit in that chair please?

Mary, you can play outside if you like.

Can I ask you a question?

You can't go to the park. It will still be wet from the rain last night.

We can't leave the room until the assignment is completed.

5. Can't: Something that is forbidden or not allowed

We cannot park the car next to this fire hydrant.

You can't drive as fast as you want in the city. There are speed limits.

You can't smoke in the restaurant.

You cannot drive a car without a license.

6. Can't: when you are sure that something isn't true or something is surprising

It can't be dark outside! It's only 4.30pm!

They can't have landed on the moon, I'm sure it's a hoax.

For more examples, including how to make questions, see our grammar notes about Can - Cannot. You might also want to see our Can - Can't - Cannot Game

COULD

Could is similar to Can and often replaces Can in the past tense (though not always)

1. To express ability in the past

I could ride a horse when I was younger but now I can't.

She could juggle eight balls when she was only 10 years old.

He could read when he was three years old.

2. Polite word used to ask for permission or to request something (in the present)

Could I please use your bathroom?

Could we move on to the next topic now please?

Could you pass me the salt please?

I'm busy right now. Could you call back later?

3. General permission in the past

In high school, we couldn't leave the classroom without a pass.

He couldn't go to the concert because his mother wouldn't let him.

4. A suggestion when asked what to do (choices and opportunities)

He could try and fix it himself.

We could go to the movies if you are interested.

5. Couldn't: Sure that something is untrue

Just like can't, you can use couldn't when you are sure that something isn't true or real.

That couldn't be my cat meowing outside, it was hit by a car last week.

He couldn't have painted that. He has no artistic ability at all.

6. Could + have + past participle: To express a possibility in the past

To express that something was possible but did not happen.

We were lucky because it could have rained but it didn't.

Why did you do that? You could have broken your leg.

7. Could + have + past participle: Unrealised past ability

This is used to say that someone was able to do something, but they did not try to do it. Sometimes this is a form of criticism.

She could have married anyone she wanted to.

Why did you sit there doing nothing? You could have helped me.

8. Could: A conditional form of Can

Would + Can = Could. Note: Would be able to can replace could in the following examples.

If we had some oranges I could make you some fresh juice.

I could write the letter if you told me what to include.

Can vs Could Summary Chart

Modals of Ability: Can, Could, Be able to, May, Might

Introduction

These five verbs are examples of modal verbs.

can

could

be able to

may

might

Modal verbs are helping/auxiliary verbs that express ideas like ability, permission, possibility, and necessity. Many modal verbs have more than one meaning. They are always followed by the simple form of a verb. For example,

Alan can swim well.

This shows that Alan has the ability to swim.

1. Modals for Ability

Let’s start with expressing ability! We use can, be able to and could to show that someone has (or doesn’t have) an ability to do something.

Look at these examples:

Present/Future Ability Negative        Past Ability    Negative

Alan can swim well.   Jackie cannot play piano.        Paul could speak Chinese when he was a child.           Mary couldn’t finish her homework last night.

I can meet you after school. We can’t visit Vancouver this weekend.         Last night, there were no clouds in the sky and they could see all the stars.          You couldn’t find the website this morning, could you?

I am able to speak two languages.     I am not able to speak Arabic. When I was a young child, I wasn’t able to tie my shoes. I wasn’t able to finish my test yesterday.

Brenda is able to run quickly. Stacey isn’t able to finish a marathon. Shaun was able to complete the assignment. Paula wasn’t able to pass the class.

You are able to program a computer. We aren’t able to make a reservation tonight. They were able to catch six fish on their trip.       You weren’t able to understand the answer, were you?

Did you notice that the verbs after “can/could/be able to” are always in the simple form? For example:

Alan can swim well. (subject + auxiliary verb + simple verb + ...)

Do NOT change the modal auxiliary OR the main verb for he/she/it subjects. In addition, do not add “ing” or “ed”.

Alan can swims well. arrrow to the right Wrong!

Alan can to swim well. arrrow to the right Wrong!

Alan can swimming well. arrrow to the right Wrong!

Alan could swam well. arrrow to the right Wrong!

How can we make questions about ability? It’s easy!

Modal auxiliary + subject + main verb + ... ?

Can she play guitar?

Could you speak English when you were a child?

BE + subject + able to + main verb + ... ?

Are you able to understand the homework?

Were you able to finish the test?

Was he able to pass the exam?

Notice that we do not need the verbs “do/does/did” when we make questions!

The modal verb “be able to” includes the word “to”; the “to” is not an infinitive.

2. Modals for Possibility

Let’s learn about expressing possibility now.

The verbs may, might and could show possibility now and in the future. In this case, they have the same meaning.

Look at this conversation:

A: My mother said that it may snow tomorrow.

B: Really? It might snow?! That’s great! I could make a snowman or go for a “snow” walk.

A: Don’t get too excited. If the temperature is high, it may not snow. It may rain.

B: Well, I guess I could still go for a walk in the rain.

Be careful with may + “be” and “maybe”. Compare these sentences. Both are correct.

Ann is not here today. She may be sick. arrrow to the right “may be” is a modal.

Ann is not here today. Maybe she is sick. arrrow to the right “Maybe” is an adverb.

3. Modals for Permission

Finally, let’s look at ways to ask for and give permission. We use may, could and can to do this.

Formality       Example

most formal/polite    May I go to the washroom?

*only used with “I” and “we”

medium formal           Could I borrow your dictionary?

Could he pay you tomorrow?

casual Can I call you back later?

Can she have a cookie?

Now, look at the (main) verbs that come after the subject. They are always in the simple form, just as with other modal verbs.

Again, the most polite/formal way to answer these questions is with “may.”

Examples:

May I go to the washroom?  Yes, you may (go to the washroom).

Yes, you can. No, you may not.

No, you cannot.

Can she have a cookie?           Yes, she can. No, she can’t.

Notice that we do not “contract” may + not = mayn’t. arrrow to the right Wrong!

Can’t and couldn’t are common contractions, however.

Modals of Ability 1 - Can, Could, Be able to, May, Might

Click on the box beside the best answer.

SHOW ONE AT A TIME

1. I'm going to bring an umbrella today because it ____________ rain.
1. ? is able to
2. ? can
3. ? might
2. The family can't decide where to go on vacation. They ____________ go to Los Angeles or they ____________ go to Hawaii.
1. ? might / may
2. ? could / couldn't
3. ? may / are able to
3. My cat ____________ jump, but it ____________ talk.
1. ? can / can't
2. ? can't / can
4. ____________ I borrow your dictionary?
1. ? May
2. ? Am I able to
3. ? Might
5. ____________ you play the piano when you were a child?
1. ? May
2. ? Can
3. ? Could
6. The little girl asked, "Mommy, ____________ I have a cookie?" The mother said, "Yes, you ____________."
1. ? may / might
2. ? can / can
3. ? can / are able to
7. Peter ____________ swim when he was a child, but now he ____________. In fact, he swims every day!
1. ? could / can't
2. ? couldn't / can
3. ? couldn't / can't
8. ____________ dogs fly? No, of course not!
1. ? Do can
2. ? Can
3. ? May
9. George is absent from class today. He ____________ be sick.
1. ? could
2. ? can
3. ? is able to
10. She ____________ understand Korean very well, but she ____________ speak it perfectly.
1. ? be able to / cannot
2. ? is able to / cannot
3. ? is able to / is able to
11. Sara ____________ Italian food and she ____________ French food too!
1. ? can cooking / can cooking
2. ? can cooks / can cooks
3. ? can cook / is able to cook
12. Kevin was disappointed because he ____________ get tickets for the football game.
1. ? wasn't able to
2. ? weren't able to
13. When Vera was young, she ____________ type quickly. She took a typing class and now she ____________ type very quickly!
1. ? can / could
2. ? could not / can to
3. ? could not / can

Modals of Ability 2 - Can, Could, Be able to, May, Might

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