Imperfect subjunctive         Practice exercises         Uses of the subjunctive

Formation

1. Take the 'they' form of the preterite.
2. Remove the -ron.
3. Add either set of endings. (The -ra endings are more commonly used.   However, with one exception, the two sets of endings are completely interchangeable.)

N.B. All verbs in Spanish follow the above rules for formation of the imperfect subjunctive.   There are no exceptions!