Can and Could: Ability, Requests and Permission

Quick Answer: Use can for present ability ("I can swim"), permission ("You can go now") and requests ("Can you help me?"). Use could for general past ability ("I could read at four"), more polite requests ("Could you open the window?") and uncertain possibility ("It could rain later"). Both are followed by the base verb without to, and neither ever takes -s.

Key takeaways

• Can and could keep one form for every subject: he can, she could, never cans or coulds.
• After can and could, use the bare verb: "I can speak", not "I can to speak" or "I can speaking".
• Could is the past of can only for general ability; for one specific past success, use was able to or managed to.
• Could you ...? is more polite than Can you ...?, and May I ...? is the most formal way to ask permission.
• Can has no future or perfect form, so say "I will be able to", never "I will can".
• Make questions by inversion ("Can you swim?") and negatives with not ("can't", "couldn't"), never with do.

What are the grammar rules for can and could?

Rule	Correct	Wrong
Same form for all subjects	She can drive.	She cans drive.
Base verb after the modal	I can speak French.	I can to speak French. I can speaking French.
Negative with not	I cannot, I can't swim.	I don't can swim.
Question by inversion	Can you swim?	Do you can swim?

Negative forms: can, cannot (one word), can't; could, could not, couldn't. See English contractions for more short forms.

Pronunciation note

In positive sentences, can is usually weak and short: "I kn swim." In negatives, can't is strong and stressed. In American English can't sounds like "kant"; in British English it sounds like "kahnt." Listen for the stress to hear the difference.

1. How do you use can and could for ability?

Present ability: can

• I can play the guitar.
• She can speak three languages.
• Can you cook?
• He can't drive.

Past ability: could

Use could for general ability in the past.

• When I was young, I could run very fast.
• She could read when she was four.
• I couldn't swim until I was twelve.

Be able to

Can has no infinitive, future or perfect form. Use be able to for those.

• I will be able to help you tomorrow. (future)
• I have never been able to whistle. (present perfect)
• I'd like to be able to speak English fluently. (infinitive)

For a single specific success in the past, use was able to or managed to, not could:

• The fire was big, but everyone was able to escape. (not "could escape")
• Couldn't is fine in the negative: "I couldn't find my keys."

2. How do you ask for permission with can, could and may?

Asking for permission

Form	Level	Example
Can I ...?	informal, friendly	Can I sit here?
Could I ...?	polite	Could I use your phone?
May I ...?	formal, very polite	May I come in?

Giving or refusing permission

• Yes, of course you can.
• Sure, go ahead.
• Sorry, you can't park here.
• You can't use phones during the exam.

Note: we answer with can, not could. "Could I borrow your pen?" "Yes, you can." Not "Yes, you could."

3. Requests

When we ask someone to do something, we use can or could.

• Can you pass the salt?
• Could you speak more slowly, please?
• Could you possibly help me with this box? (extra polite)

Adding "please" and using could makes requests softer. Our guide to polite requests in English shows more options like "Would you mind ...?"

4. Possibility

Could shows that something is possible but not certain.

• It could rain this afternoon. Take an umbrella.
• That could be the answer.
• Don't touch it, it could be dangerous.

Can shows general possibility, things that are sometimes true.

• Winters in Erzurum can be very cold.
• Learning a language can be difficult.

Couldn't can also mean something is impossible:

• She couldn't be at work, I just saw her at the market.

5. Suggestions

Could is often used to make gentle suggestions.

• We could go to the cinema tonight.
• You could try asking your teacher.
• If you're tired, you could take a nap.

Can vs could at a glance

Use	can	could
Present ability	I can swim.
Past ability		I could swim at five.
Permission	Can I go?	Could I go? (more polite)
Requests	Can you help?	Could you help? (more polite)
Possibility	general: It can be cold.	specific: It could be cold tomorrow.
Suggestions		We could eat out.

What are the most common mistakes with can and could?

Mistake	Wrong	Right
To after can	I can to speak English.	I can speak English.
-s after can	He cans help.	He can help.
Do with can	Do you can come?	Can you come?
Could for one specific success	After two hours I could find the hotel.	After two hours I was able to find (managed to find) the hotel.
Will with can	I will can help.	I will be able to help. I can help tomorrow.
Could in a permission answer	Could I borrow it? Yes, you could.	Yes, you can.

A note for Turkish speakers

Turkish expresses ability with a suffix (yüzebilirim, I can swim) and politeness with forms like yardım eder misiniz. In English, ability and politeness are carried by separate words, so remember: the modal goes first, the verb stays bare. "Yüzebildim" for one successful attempt is usually "I managed to swim" or "I was able to swim", not "I could swim".

Practice Quiz

Choose can, can't, could or couldn't.

1. ___ you help me carry this, please?
2. My grandfather ___ speak English, but he ___ speak German.
3. When I was five, I ___ ride a bike.
4. It's very cloudy. It ___ rain later.
5. ___ I open the window? It's hot in here.
6. I'm sorry, I ___ come to your party last Saturday.
7. You ___ smoke here. It's a hospital.

Answers: 1. Can or Could 2. can't, can 3. could 4. could 5. Can or Could 6. couldn't 7. can't

Modal verbs come up in every conversation. Start the free LearnLingo course to practice can and could in real requests and dialogs with Sage the Turtle.

People Also Ask

What is the difference between can and could?

Can is used for present ability, permission and requests. Could is the past form for general ability, and it is also a more polite way to make requests and a softer way to talk about possibility.

Is could more polite than can?

Yes. Could you help me? is a little more polite than Can you help me? Both are acceptable in everyday situations.

Do we add -s or to after can?

No. Can and could never change for he, she or it, and they are followed by the base verb without to. Say She can swim, not She cans swim or She can to swim.

Related Reading

• How to Make Polite Requests in English
• How to Ask Questions in English
• Will vs Going To for the Future
• English Contractions: I'm, Don't, Can't