Expressing ability with can, could, and be able to
Subject + can/could + base verb; Subject + be able to + base verb
Subject + cannot/can't/couldn't + base verb; Subject + be + not + able to + base verb
Can/Could + subject + base verb? Is/Are/Was/Were + subject + able to + base verb?
💡 Use could for general past ability; was/were able to for specific past achievements.
✓She can play the piano.
✗She can to play the piano.
No 'to' after can.
✓I could run fast when I was young.
✗I can run fast when I was young.
Use could for past ability.
✓He was able to escape.
✗He could escape (specific achievement).
Use was able to for specific past success.