Explanation
Exercises

Can, could, be able to

How we talk about ability, possibility, permission and requests — with the right tense.

Quick map

Meaning
Common form(s)
Example
General ability (now)
can / can’t + base verb
I can swim. · I can’t drive.
General ability (past)
could / couldn’t + base verb
She could read at four. · We couldn’t ski.
Specific success on one occasion (past)
was/were able to / managed to
They were able to / managed to escape.
Other tenses (future, perfect, infinitive, -ing)
be able to
I will be able to join. · I haven’t been able to study. · to be able to help · being able to travel
Possibility (general)
can / can’t
Anyone can win. · I can’t come next week.
Permission
can / can’t · polite: Could I/you…?
Can I sit here? · You can’t park here. · Could you sign here?
Senses
can + see/hear/feel/smell/taste
I can hear music. · I can’t see him.

Forms & tense choices

  • can/could are modals → use the base verb (no to): can speak, could find (not to can / could to find).
  • can has only present; could is its past (and a more polite modal). For all other verb forms use be able to: will be able to, have been able to, to be able to, being able to.
  • Questions/negatives: modal + subject + base verb / modal + not + base verb: Can you help? · I can’t help. · Could she swim?

Core uses

Ability

  • General ability: He can play chess / When she was six, she could read.
  • One specific occasion (past): use was/were able to or managed to. It was foggy, but we were able to land. ✅ In the negative, couldn’t also works: We couldn’t land.

Possibility

  • General/real-world possibility: It can get very hot here.
  • Plans/uncertain future: prefer may/might at B1 (not required here, but common): I might come later.

Permission

  • can/can’t for rules: You can’t smoke inside.
  • Requests / asking permission: Can I…? (neutral/common), Could I…? (more polite).
  • Other tenses use be allowed to: When I was a child, I wasn’t allowed to stay out late. · Will we be allowed to leave early?

Requests

  • Can you open the window? (friendly) · Could you possibly open the window? (politer).

Senses & stative verbs

  • With perception verbs, use can, not continuous: Can you hear that? ✅ / Are you hearing that? ❌

Contrasts & common pitfalls

  • Specific past success: We were able to fix it / We managed to fix it (not usually we could fix it for one event).
  • Infinitive/gerund: use be able to: I’d like to be able to play · Being able to work remotely is great.
  • Politeness scale (requests): Can you…? → neutral/common; Could you…? → more polite.
  • Logical impossibility (present) at B1 is often heard with can’t: It can’t be Tom — he’s abroad.

Mini summary

Use can/could for general ability, possibility, permission and requests. For other tenses (future, perfect, infinitive, -ing), switch to be able to. For one successful event in the past, say was/were able to or managed to (negative: couldn’t is fine). With senses, prefer can + verb. In requests, could is politer than can.

Exercises:
1
2
3

Can, could, be able to: Ability and possibility

Choose the correct form of can, could, be able to (affirmative or negative). Use a form of be able to only if a form of can or could is not possible.
1
Can you read this label for me? I drive at night; the glare from headlights blinds me.
2
I’ve never swim very well.
3
After two years in China, I speak quite fluently now.
4
I hate not join my friends when I’m on the late shift.
5
When he was forty, he speak six languages.
6
After six hours of climbing, we reach the very top.
7
By the end of the summer, I ride a bike without help.
8
I’ve called three times today, but I get through to the doctor.
9
Once the roadworks finish next week, we drive straight through.
10
Take a jacket — the weather turn really cold this evening.

Can, could, be able to: Ability and possibility

Choose the correct option/s for each gap below. Use can or could if possible.
1
_____ you possibly turn the music down?
A.
B.
C.
2
Sharks _____ smell tiny amounts of blood in water.
A.
B.
C.
3
After two hours of searching, we _____ find the missing file.
A.
B.
C.
4
I _____ open the door yesterday; it was stuck.
A.
B.
C.
5
Take an umbrella; it _____ rain later.
A.
B.
C.
6
If you practise every day, you _____ pass the exam next month.
A.
B.
C.
7
So far, I haven’t _____ reach the landlord.
A.
B.
C.
8
Thanks to the new update, we _____ export PDFs directly now.
A.
B.
C.
9
By midnight the engineers _____ restore the service.
A.
B.
C.
10
I’m busy in the morning, but I _____ reply to your email this afternoon.
A.
B.
C.

Can, could, be able to: Ability and possibility

Fill in the gaps with the correct form of can, could, be able to (affirmative or negative). Use a form of can or could if possible.
1
you open the window, please?
2
I’ve tried three times, but I haven’t reach the site.
3
When I was ten, I swim across the lake.
4
After an hour of searching, we finally find the keys.
5
Marta speak six languages fluently.
6
Sorry I come yesterday — I was ill.
7
Do you think you finish the project by Friday?
8
If the weather clears, we go for a hike this afternoon.
9
By next summer, I’ll drive a manual car.
10
It was pitch dark, so she see anything.