Past ability: could / couldn't / was able to

Rules

• Rule 1: could + base verb

  After could the verb is always in the base form, and could never changes with the subject.

  Pattern: subject + could + base verb

  Example: She could read at four.

  Example: They could hear the birds.

• Rule 2: couldn't (could not)

  We say we were not able to do something with couldn't. There is no such thing as didn't could!

  Pattern: subject + couldn't + base verb

  Example: I couldn't open the jar.

  Example: We couldn't go out because of the rain.

• Rule 3: questions and short answers

  In a question Could comes first. Short answer: Yes, I could. / No, I couldn't.

  Pattern: Could + subject + base verb?

  Example: Could you swim at six? – Yes, I could.

  Example: Could he see the board? – No, he couldn't.

• Rule 4: was / were able to

  To say we managed to do something in one particular situation, we use was / were able to. In positive sentences we usually don't use could for one success (except with verbs like see and hear). In negatives couldn't always works.

  Pattern: I / he / she / it was able to · you / we / they were able to

  Example: The river was deep, but we were able to cross it.

  Example: She was able to climb to the top.

Common mistakes

• I could swam. → I could swim.

  After could the verb is base.

• She coulds dance. → She could dance.

  could never takes -s.

• We were able open it. → We were able to open it.

  to follows able.