Ability
Can someone do it?
Meaning
Ability tells us what someone can do, whether learned or not. It covers learned skills as well as what someone's body or mind allows them to do. Languages express it with helper verbs, endings, or ordinary phrases, and some have no special form for it. Unlike Permission, Ability concerns what someone can do, not what they are allowed to do.
How to spot it
Check whether the message says someone has the skill or capacity to do something, rather than merely being allowed to do it.
In your native language
English commonly expresses ability with can followed by a verb without to. Could often describes general ability in the past, while was/were able to usually describes success on one occasion. Be able to also allows forms such as will be able to for future ability.
I can ride a bike.
Can expresses a skill, and ride follows without to.
When I was ten, I could swim across the pool.
Could describes an ability the speaker had at that age, not one particular swim.
The door was stuck, but we were able to open it.
Were able to shows that opening the door succeeded on this occasion.
In your learning language
Spanish normally uses saber followed by an infinitive for a learned skill, and poder followed by an infinitive for capacity or the ability to act in particular circumstances. The infinitive is a verb form such as nadar with no person ending; saber or poder changes to show who can do it and when. There is no preposition between either verb and this infinitive.
Mi hermana sabe conducir.
My sister knows how to drive.
Hoy no puedo correr; me duele la rodilla.
I can't run today; my knee hurts.
Poder describes what the speaker's physical condition allows today.
Sé nadar, pero aquí no puedo nadar: la piscina está cerrada.
I know how to swim, but I can't swim here: the pool is closed.
Saber names the skill; poder describes what the circumstances allow.
Learners whose language uses one verb for both a learned skill and practical capacity may overuse poder where saber is more natural. Learners whose language links two verbs with a preposition may add one, as in *sé a nadar.