Grammar. Can and could.
1. Usaremos can y su negación can’t / cannot para expresar habilidad.
1.1. Oración afirmativa.
Todd can surf well.
1.2. Oración negativa.
Knox can’t swim well.
1.3. Oración Interrogativa.
Can Neil play the drums?
2. Could, and its negative form couldn't / could not are the past and conditional of can. Use it for:
a. Polite requests. → Could you open the door, please?
b. Past ability. → My brother could run fast when he was 20.