English — Ability: can / could / be able to
To talk about ability, English uses can for the present, could for general past ability, and was/were able to or managed to for a single thing you succeeded in doing. Be able to fills the tenses that can and could lack.
How it works
Can and could are modal verbs: they take a bare infinitive and never add -s (I can swim, she can swim). Could is the past of can for a general skill you had over time — I could read at five. For a specific success on one occasion, use was/were able to or managed to — After an hour, we were able to open the door / we managed to open the door. Because can and could have no infinitive or participle, other tenses borrow be able to — will be able to, have been able to.
Examples
| Form | Use | Example |
|---|---|---|
| can | present ability | I can swim. |
| can't / cannot | present inability | She can't drive yet. |
| could | general past ability | I could read at five. |
| was / were able to | specific past achievement | I was able to open the door. |
| managed to | past success with effort | We managed to catch the train. |
| will be able to | future ability (borrowed form) | You will be able to join us. |
| have been able to | perfect ability (borrowed form) | I haven't been able to sleep. |
Good to know
In positive sentences, do not use could for a single past success: not I could open the door yesterday but I was able to open the door / I managed to open the door. Could is fine for a general skill (I could swim as a child) and in the negative even for a single event — I couldn't open the door works.