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.

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.

3. To offer to do something for others

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

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.

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

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

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

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

3. General permission in the past

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

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.

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

To express that something was possible but did not happen.

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.

8. Could: A conditional form of Can

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

Can vs Could Summary Chart

Can and Could in English


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See our more simple notes about Can and Cannot.

See our notes about other Modal Verbs.


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