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Grammar, compared

Can vs could vs be able to

Can is for ability and permission now. Could is for general ability in the past or a polite request. Be able to fills the gaps can and could cannot cover.

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The short answer

Can, could / Be able to
Can, couldBe able to
I can swim. (ability now)I was able to swim across the lake yesterday. (one specific past success)
Could you help me? (polite request)Will you be able to help me tomorrow? (future ability)
I could swim when I was five. (general past ability)I was able to finish the report on time. (one specific past success)

When to use each

Can, could and be able to compared
PointCan / couldBe able to
Present abilitycan: I can drive.am/is/are able to: I am able to drive. (more formal)
General past abilitycould: I could read at four.was/were able to: I was able to read at four.
One specific past successNot used in a positive sentencewas able to, or managed to: I was able to fix it.
Future abilityNot used, can has no future formwill be able to: I will be able to finish by Friday.
Polite requestCould you...? Can you...? (less formal)Not used for requests

Watch out if you speak Spanish

  • For one finished success in the past, could does not work in a positive sentence. Say was able to or managed to, not I could pass the exam.
  • Could works fine in the negative for one past event: I couldn't find my keys.
  • No future form of can exists, so use will be able to: I will be able to come, not I will can come.
  • Pude covers all of this in Spanish, so check the sentence: a general ability uses could, one specific success uses was able to.

Practice

Grammar practice

Choose or type the answer for each sentence, then check.

  1. 1. I speak three languages.
  2. 2. When I was a kid, I climb trees easily.
  3. 3. After months of practice, she finally run a marathon.
  4. 4. I'm sorry, I come to the meeting tomorrow.
  5. 5. you pass me the salt, please?

  6. 6. I

    swim by the time I was six.

  7. 7. She

    finally fix the printer after an hour.

  8. 8. I

    be able to come, I'll let you know tomorrow.

0 of 8 checked

Questions

Why can't I say I could pass the exam for one event?
Could only works for general ability or in the negative. For one specific past success, use was able to or managed to: I was able to pass the exam.
What is the future of can?
Can has no future form, so use will be able to: I will be able to help you tomorrow.

Keep going

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