The imperfect subjunctive

The imperfect subjunctive is always derived from the pretérito indefinido, ellos/ellas form: remove the ending -ron and add the correct ending.

This also works for irregular verbs, because you start from a form you already know:
- tener → tuvieron → tuvier-
- ir/ser → fueron → fuer-
- pedir → pidieron → pidier-

This way you automatically carry over any irregularities from the preterite.

There are two equivalent endings: -ra (hablara) and -se (hablase). Both are grammatically correct and mean the same thing.

• The -ra form is by far the most common, in both Spain and Latin America.
• The -se form sounds more formal or literary and appears more often in written language.

Only the -ra form has an extra function: it can replace the conditional with a small group of verbs (see the section on politeness).

When the main clause is in a past tense (pretérito indefinido, imperfecto, pluscuamperfecto or condicional) and the subordinate clause requires the subjunctive (wish, doubt, emotion, impersonal expression...), the subordinate clause takes the imperfect subjunctive — never the present subjunctive.

Typical triggers: querer que, pedir que, esperar que, dudar que, no creer que, era importante que, era posible que...

After como si (as if) you always use the imperfect subjunctive (or pluscuamperfecto de subjuntivo for the past) — never the indicative, even when talking about the present.

With the verbs querer, poder and deber, the -ra form of the imperfect subjunctive is used as a polite alternative to the conditional. It sounds softer and more formal.

• quisiera = would like (more polite than quiero)
• pudiera = would be able to
• debiera = should