When we talk about an ability, we need to distinguish between a:
•General ability – This is something that once you have learned you can do any time you want, like being able to read or swim or speak a language, for example.
•Occasional ability – This means something that you can or can’t do in one particular situation. For example, being able to lift something heavy, or find somewhere you are looking for.
How do we talk about abilities?
•Can / Can’t / Be able to – We use all of them to talk about general and occasional abilities
👉 I can play the piano
👉 She can speak English
👉 We can’t come now
👉 He called us because he wasn’t able to find the house
👉 I’m able to whistle!
•Could / Couldn’t – We use them to talk about a general ability in the past
👉 I could read when I was four
👉 He couldn’t dance at all until he took lessons
👉 My grandfather couldn’t swim
Be careful! We can also use couldn’t to talk about occasional abilities but with a meaning of possibility, but not could
👉 I couldn’t buy milk yesterday → No pude comprar leche ayer, no me fue posible
👉 She couldn’t arrive on time → No pudo llegar a tiempo pero podría haberlo conseguido
👉 They couldn’t pass the exam → No aprobaron el examen pero podrían haberlo hecho si hubiesen estudiado más