- Our bay will be able to walk in a few weeks. Can you/Are you able type? I can’t pay you today. Can you wait till tomorrow? (O bien: Could you wait?). Since his accident he hasn’t been able to leave the house.
[can y be able: shall/will be able es la única forma en futuro. En el presente se pueden usar tanto can como am able; can es la forma usual. En el pretérito perfecto solo se puede usar la forma be able.]
2. Could you run the business by yourself? (if this was necessary); Could he get another job? (if he left this one). I could get you a copy, (if you want one). Could you show me the way/lend me L5/wait half an hour?; Could you please send me an application form? HOUSEHOLDER: Could you come and mend a leak in a pipe? PLUMBER: Would sometime next month suit you? HOUSEHOLDER: Couldn’t you come a little earlier?
[could: could puede usarse con un significado presente cuando hay idea de condición; en los dos primeros ejemplos could es reemplazable por would be able. could you? Es una estupenda manera de introducir una petición. Es una alternativa a would you? y un poco más educado. couldn’t you? es también útil.]
3. When I was young I could/was able to climb any tree in the forest. Although the pilot was badly hurt he was able to explain what had happened (He could and did explain); The boat capsized quite near the bank so the children were able to swim to safety, (They could and did swim). He read the message but he couldn’t/wasn’t able to understand it; I could/was able to see him through the window.
[could y was able usados para expresar capacidad en el pasado: para expresar unicamente capacidad puede usarse cualquiera de las dos formas; para «capacidad» + una acción determinada, se emplea was able. Esta regla se relaja en la negativa si la acción no ha tenido lugar, y con verbos de los sentidos.]
4. He said he had lost his passport and hadn’t been able to leave the country.
[had been able es la forma del pluscuamperfecto.]
A Practical English Grammar (A.J. Thomson & A.V. Martinet) 