Voces pasiva y activa
Las oraciones escritas en voz pasiva son más fáciles de entender que las escritas en pasiva. Cambiar de la voz pasiva a la voz activa es bastante sencillo pero requiere cierta práctica. En la tabla de equivalencias que se muestra a continuación, podemos comprobar que el tiempo verbal de "to be" en la voz pasiva es siempre el mismo que el tiempo del verbo principal. Para emplear la voz activa, es necesario explicitar el sujeto que realiza la acción.
"To keep", voces activa y pasiva
| Tiempo verbal | Voz activa | Voz pasiva | Oración en activa | Equivalente en pasiva |
|---|---|---|---|---|
| Simple present | keep | is kept | I keep the butter in the fridge. | The butter is kept in the fridge. |
| Present continuous | is keeping | is being kept | John is keeping my house tidy. | My house is being kept tidy. |
| Simple past | kept | was kept | Mary kept her schedule meticulously. | Mary's schedule was kept meticulously. |
| Past continuous | was keeping | was being kept | The theater was keeping a seat for you. | A seat was being kept for you. |
| Present perfect | have kept | have been kept | I have kept all your old letters. | All your old letters have been kept. |
| Past perfect | had kept | had been kept | He had kept up his training regimen for a month. | His training regimen had been kept up for a month. |
| Simple Future | will keep | will be kept | Mark will keep the ficus. | The ficus will be kept. |
| Conditional Present | would keep | would be kept | If you told me, I would keep your secret. | If you told me, your secret would be kept. |
| Conditional Past | would have kept | would have been kept | I would have kept your bicycle here if you had left it with me. | Your bicycle would have been kept here if you had left it with me. |
| Present Infinitive | to keep | to be kept | She wants to keep the book. | The book wants to be kept. |
| Perfect Infinitive | to have kept | to have been kept | Judy was happy to have kept the puppy. | The puppy was happy to have been kept. |
| Present Participle / Gerund | keeping | being kept | I have a feeling that you may be keeping a secret. | I have a feeling that a secret may be being kept. |
| Perfect Participle | having kept | having been kept | Having kept the bird in a cage for so long, Jade wasn't sure it could survive in the wild. | The bird, having been kept in a cage for so long, might not survive in the wild. |