Understanding Modal Verbs: Can/Can't
Can is a helper verb. It goes before another verb. We use can and can't for ability, possibility, permission, offers and requests.
Structure
The base form is the verb without to or -s: swim, go, play. Can has the same form for I, you, he, she, we and they.
- Positive: subject + can + base form. Example: She can swim.
- Negative: subject + can't + base form. Example: He can't drive.
- Question: Can + subject + base form? Example: Can you play the guitar?
- Short answer: Yes, I can. / No, I can't. Example: Can you swim? Yes, I can.
Can't is the short form of cannot. Write cannot as one word.
How the Grammar Works
- Put can before the base form of the verb. Example: I can speak English.
- Do not add -s to can or to the next verb. Example: He can swim.
- For a question, put can before the subject. Do not use do or does. Example: Can she swim?
- Use can for ability. Can't means 'not able to'. Example: I can't dance.
- Use can for possibility. Can't means something is not possible. Example: She can't come today.
- Use can for permission. Can't means 'not allowed to'. Example: You can't park here.
- Use Can I...? for offers and Can you...? for requests. Example: Can I help you?
Common Use Cases
- Ability: I can swim.
- No ability: He can't drive.
- Possibility: She can't come to the party.
- Asking for permission: Can I use your phone?
- Giving permission: You can use my phone.
- Saying no to permission: You can't park here.
- Offering help: Can I help you?
- Asking someone to do something: Can you help me, please?
Frequent Mistakes and How to Avoid Them
- I can to swim. - correct: I can swim. Do not use to after can.
- He cans swim. - correct: He can swim. Can never takes -s.
- She can swims. - correct: She can swim. Use the base form after can.
- Do you can swim? - correct: Can you swim? Do not use do with can.
Comparison with Related Grammar
Can is for now. Could is for the past: I could swim at five. Could is also a more polite request: Could you help me, please?
Example Sentences
- She can dance very well.
- We can't go to the park today.
- Can you speak French?
- You can use my phone.
- You can't park here.
- Can I help you?
- Can you help me, please?
- They can't find their keys.
When to Use This Rule
Use can and can't to talk about what you or other people are able or allowed to do, and to make offers and requests.