Use can for ability, permission and possibility. Use could for ability in the past and for polite requests. Use have to when something is necessary, like a rule at work or something you need to do.
The pattern
I can speak Spanish.
She has to work on Saturday.
01Can and can't
Use can + base verb for ability (I can swim), permission (You can park here) and possibility (You can buy tickets online). The form is the same for every person: he can, never he cans. The negative is can't or cannot.
- My roommate can cook really well.
- Can I use your charger?
- You can't smoke in the building.
- Can you hear me?
02Could: past ability and polite requests
Could is the past of can: I could read before I started school. The negative is couldn't.
Could also makes a request sound more polite than can. Use Could you...? with coworkers, customers and people you don't know well.
- I couldn't find a parking spot this morning.
- When I was in college, I could stay up all night.
- Could you send me the file, please?
- Could I ask you a question?
03Have to and don't have to
Use have to or has to + base verb when something is necessary. For the past, use had to. Questions and negatives use do, does or did.
Be careful: don't have to means it's not necessary. It does not mean you can't.
- I have to be at work at 8:00.
- Does she have to wear a uniform?
- We had to wait an hour at the DMV.
- You don't have to tip at a fast food counter.
| Meaning | Present | Past |
|---|---|---|
| ability | can, can't | could, couldn't |
| it's necessary | have to, has to | had to |
| it's not necessary | don't have to, doesn't have to | didn't have to |
04Common mistakes
She cans drive.
She can drive.
Can never takes -s.
I can to help you.
I can help you.
After can and could, use the base verb without to.
He have to work late.
He has to work late.
With he, she and it, use has to.
You don't have to smoke here. It's not allowed.
You can't smoke here. It's not allowed.
Can't means it's not allowed. Don't have to means it's not necessary.