Use the imperfect subjunctive in the same contexts as present subjunctive, but when the main clause is in the past. Also used for contrary-to-fact conditions (si clauses).
Important Rules
•Based on the ellos form of preterite: remove -ron, add endings
•Two forms exist: -ra/-ras/-ra/-ramos/-rais/-ran (more common)
•Or: -se/-ses/-se/-semos/-seis/-sen (more formal)
•If preterite is irregular, imperfect subjunctive is irregular