Can, Could, Be Able to

Exercises

Explanation

1. CAN — Present Ability, General Possibility, Informal Permission

A. Present ability (skills or natural ability)

We use can to describe what someone is capable of doing now.

• She can solve difficult math problems.

• I can use this software without help.

• Can your brother play the piano?

B. General possibility (something that is sometimes true)

Can shows that something is possible in general, not in one specific moment.

• This road can get very busy during the day.

• Winter in this city can be extremely cold.

• These plants can grow very fast in good weather.

C. Permission (informal or friendly)

We use can to ask for or give permission in everyday conversation.

• Can I sit next to you?

• You can leave your bag here.

• Can we start the meeting now?

Negative forms: cannot / can’t

Examples:

• I can’t remember his name.

• You can’t enter this area without a pass.

Questions:

• Can I ask you something?

• What can we do to help?

2. COULD — Past Ability, Polite Requests, Possibility

Although could is the past form of can, it also has several other important uses.

A. Past general ability

We use could to talk about abilities someone had in the past.

• I could run very fast when I was a child.

• She couldn’t swim until she was twelve.

• Could you speak English before you moved here?

B. Polite requests (more polite than can)

Could often sounds softer and more polite.

• Could you close the door, please?

• Could I borrow your notes for a moment?

C. Possibility (less certain than “can”)

Could expresses something that is possible, but not sure.

• We could visit the museum this afternoon.

• It could snow later tonight.

D. Criticism or missed opportunity (could + have + V3)

Use this when something did not happen, but you think it should have.

• You could have told me the truth.

• They could have warned us earlier.

Negative forms: could not / couldn’t

Examples:

• I couldn’t finish the project yesterday.

• She couldn’t believe what she heard.

3. Expressing Doubt, Surprise, or Impossibility

We sometimes use can and could in questions or negative forms to show doubt or disbelief.

Present doubt

• Can this be the right address?

• Can he be joking?

Past doubt

• Could she have been correct after all?

• Could he have lived abroad for so long?

Expressing impossibility (strong disbelief)

• That can’t be true.

• She can’t be talking about us.

• He couldn’t have written that message.

• They couldn’t have left so quickly.

4. BE ABLE TO — Ability in All Tenses

Can has no future form, so we use be able to instead. It also works well for specific situations in the past.

A. Future ability

• I will be able to attend the meeting next week.

• She will be able to drive after her exam.

• They will be able to move in next month.

B. Past ability in a specific moment

Use was/were able to for success in one situation.

• We were able to catch the last train.

• He wasn’t able to repair the printer.

• Were you able to find the address?

C. Present ability (more formal than “can”)

• I am able to answer your questions now.

• She is able to work independently.

Can vs. Be able to

• Can = general ability
  I can swim. (I know how)

• Be able to = ability in one specific moment
  I was able to swim across the lake yesterday.

5. Positive, Negative, and Question Forms

6. Useful Expressions with “Can / Could”

A. can’t help + -ing = unable to stop oneself

• I can’t help laughing at this joke.

• She couldn’t help smiling when he arrived.

B. can’t possibly = it is impossible

• I can’t possibly finish this by midnight.

• She couldn’t possibly agree to that proposal.

C. can’t but + base verb = have no choice (formal)

• I can’t but accept the situation.

• He couldn’t but apologize.

7. Everyday Examples

Ability

• My cousin can repair old computers.

• When I lived in France, I could understand everyday conversations easily.

Permission

• Can I have a glass of water?

• Could I take this seat?

Possibility

• The streets can get very crowded during the festival.

• It could be warmer tomorrow.

Requests

• Can you send me the details?

• Could you wait a moment, please?

Future ability

• After some practice, you will be able to play this song.

Quick Summary

• can: present ability, possibility, informal permission

• can’t: impossibility or prohibition

• could: past ability, polite requests, weaker possibility

• could have + V3: criticism or missed opportunity

• be able to: ability in all tenses, especially future or specific situations