Forming the Spanish Imperfect Subjunctive
Start with the third-person plural form of the preterit.
Drop the -ron ending to establish the verb’s imperfect subjunctive base.
This verb base is used for all verbs whether they’re regular, irregular, stem-changing, or spelling-changing verbs.
Add the common endings from one of the lists that follow.
These endings are uniform for -ar, -er, and -ir verbs. You can use either set of endings; they both give you the imperfect subjunctive.
The vowel that precedes the nosotros ending is always accented.
In Spanish, you use the imperfect subjunctive to express uncertainty about the past. Hindsight isn’t always 20/20; sometimes it’s more like 50/50. You may believe that something happened or hope it happened rather than knowing it happened. The good news is that unlike the indicative past tense, which gives you the choice between the preterit and the imperfect, the subjunctive uses only the imperfect. Whenever the verb in the main clause is in the past tense (whether preterit, imperfect, or past perfect), the subordinate clause uses the imperfect subjunctive. Here are a couple examples:
Mi padre dudaba que nosotros comiéramos toda la pizza. My father doubted that we ate the whole pizza.
Ellos deseaban que su hermano abriera la puerta. They wished that his brother would open the door.