be able to

Rules

• Rule 1: be able to = can

  In the present, am / is / are able to + base verb means the same as can. In everyday speech we usually say can in the present; be able to does its real job in the other tenses.

  Pattern: subject + am / is / are + able to + base verb

  Example: My sister is able to read long books.

  Example: Dolphins are able to jump very high.

• Rule 2: Future → will be able to

  can has no future form. Never say ~~will can~~; say will be able to. Negative: won't be able to. Question: Will + subject + be able to…?

  Pattern: will / won't + be able to + base verb

  Example: One day we will be able to visit the moon.

  Example: I won't be able to come on Friday.

• Rule 3: Present perfect → have / has been able to

  For an ability that started in the past and is still true, or something managed up to now, we use have / has been able to. It often comes with since, for, yet, never, so far. ~~have could~~ is wrong!

  Pattern: have / has + been able to + base verb

  Example: She has been able to ride a bike since she was five.

  Example: I haven't been able to finish my book yet.

• Rule 4: After to and after modals

  After verbs like want, hope, would like, need we use to be able to. After modals like might, should, must we use be able to. After enjoy, imagine or a preposition (about, without) we use being able to.

  Pattern: want to be able to · should be able to · enjoy being able to

  Example: I'd like to be able to play the violin.

  Example: You should be able to see the lake from here.

• Rule 5: Past → was / were able to

  could is for general ability in the past: When I was five, I could swim. But when we say we managed to do something once, in one situation, a positive sentence uses was / were able to (or managed to), not could. In the negative both are fine: I couldn't / wasn't able to find it.

  Pattern: was / were able to = succeeded once

  Example: The jar was tight, but Dad was able to open it.

  Example: We were able to catch the last bus.

Common mistakes

• I will can come tomorrow. → I will be able to come tomorrow.

  Two modals (will + can) can't go together.

• I want to can dance. → I want to be able to dance.

  can has no to form.

• He has could swim for years. → He has been able to swim for years.

  can / could has no past participle; use been able to.