What is it?
Can, can’t, could, and couldn’t are modal verbs.
They are used to talk about:
- present ability
- past ability
- permission
- requests
- possibility
Can is the positive form.
- I can swim.
Can’t is the short form of cannot.
- I can’t drive.
Could is often used for past ability or polite requests.
- She could read when she was four.
- Could you help me?
Couldn’t is the short form of could not.
- We couldn’t find the address.
When to use
Use can for present ability.
- He can speak English.
- I can cook.
Use can’t when someone is not able to do something.
- She can’t swim.
- We can’t come today.
Use can to ask for or give permission.
- Can I use your phone?
- You can leave early.
Use could for general ability in the past.
- I could run fast when I was younger.
- They could speak French as children.
Use couldn’t for lack of ability or an unsuccessful situation in the past.
- He couldn’t read the sign.
- We couldn’t open the door.
Use can or could to make requests.
- Can you close the window?
- Could you close the window?
Could is usually more polite than can in requests.
Structure
Use the base form of the verb after can, can’t, could, and couldn’t.
| Form | Structure | Example |
|---|---|---|
| Positive present | subject + can + base verb | She can drive. |
| Negative present | subject + can’t + base verb | She can’t drive. |
| Positive past | subject + could + base verb | She could drive at eighteen. |
| Negative past | subject + couldn’t + base verb | She couldn’t drive last year. |
The form is the same for every subject.
- I can swim.
- He can swim.
- They can swim.
Do not add -s after he, she, or it.
Questions
Use:
Can/Could + subject + base verb?
| Question type | Example |
|---|---|
| Present ability | Can you swim? |
| Permission | Can I sit here? |
| Request | Can you help me? |
| Polite request | Could you help me? |
| Past ability | Could she read at five? |
Short answers
- Can you drive? — Yes, I can.
- Can he come? — No, he can’t.
- Could they swim? — Yes, they could.
- Could she open it? — No, she couldn’t.
Examples
- I can speak a little Spanish.
- She can’t come to work today.
- Can you help me with this box?
- Can I open the window?
- You can use my computer.
- He could swim when he was five.
- We couldn’t find a taxi last night.
- Could you speak more slowly, please?
- They could not hear the announcement.
- My brother can cook very well.
Exceptions
Use could for general past ability.
- She could play the piano when she was young.
For one specific successful action in the past, was able to is often more natural.
- We were able to fix the problem yesterday.
However, couldn’t is natural for a specific unsuccessful action.
- We couldn’t fix the problem yesterday.
Cannot is written as one word.
- Correct: cannot
- Incorrect: can not
The form can not is possible only when not belongs to another phrase, but this use is uncommon.
Common mistakes
-
Incorrect: She cans swim. Correct: She can swim. Explanation: Do not add -s to modal verbs.
-
Incorrect: I can to drive. Correct: I can drive. Explanation: Use the base verb without to after can.
-
Incorrect: He could speaks English. Correct: He could speak English. Explanation: Use the base form after could.
-
Incorrect: Do you can help me? Correct: Can you help me? Explanation: Do not use do in questions with can.
-
Incorrect: I don’t can swim. Correct: I can’t swim. Explanation: Use can’t, not don’t can.
-
Incorrect: She could to read at four. Correct: She could read at four. Explanation: Do not use to after could.
-
Incorrect: Can you helped me? Correct: Can you help me? Explanation: Use the base form of the verb after can.
-
Incorrect: I couldn’t found my keys. Correct: I couldn’t find my keys. Explanation: Use the base form after couldn’t.