The subjunctive form (imperfect) 1

Building the imperfect subjunctive from the preterite — Take the 3rd-person plural preterite, drop -ron, and add the endings -ra, -ras, -ra, -ramos, -rais, -ran: hablaron → habla-ra, hablaras…; comieron → comie-ra; fueron → fue-ra. Any irregularity in the 3rd-person plural preterite automatically carries into the imperfect subjunctive.

When to use it — past triggers — The imperfect subjunctive is used in subordinate clauses when the main verb is in a past tense (or conditional) and triggers the subjunctive: Quería que vinieras. Era necesario que estudiasen. Me alegró que llegara a tiempo. The "sequence of tenses" rule: past main verb → imperfect subjunctive.

-ra vs -se forms — both correct — Spanish has two sets of imperfect subjunctive endings: -ra, -ras, -ra… and -se, -ses, -se… Both are grammatically correct. The -ra form is far more common in everyday speech across the Spanish-speaking world; the -se form is mainly literary and written, especially in Spain.