Maman, tu nous avais promis de nous acheter une glace, si nous finissions nos devoirs avant cinq heures !
In the above sentence, is the verb finir in the imperfect indicative, in the present subjunctive, or in the imperfect subjunctive?
In my native Portuguese, the imperfect subjunctive is the correct verb form here, but nobody would bat an eye if, in informal speech, the imperfect indicative were used instead. Perhaps the same is true in French?
It is in the imperfect indicative, l'imparfait de l'indicatif. The subjunctive cannot be used without a relative or subordinate clause, usually beginning with que (plus ou moins). Si does not invoke the subjunctive but can invoke the conditional if...then meaning. That being said, si conditional phrases do not always mean the conditional mood.
The sequence of tenses for conditional si clauses are:
Exceptions are rare but do happen. More about si clauses here and here.
This should be the imperfect indicative: it is generally the indicative that appears in clauses introduced by si. In writing, one may see what appears to be the imperfect subjunctive in a si-clause, but this does not occur in everyday speech, and anyway, it is more precisely the pluperfect subjunctive that is sometimes used:
Le plus-que-parfait du subjonctif permet d'exprimer l'irréel du passé dans la langue soutenue. Dans un système hypothétique, il peut remplacer le conditionnel passé dans la principale et l'indicatif plus-que-parfait dans la subordonnée. On le nomme parfois, de manière erronée, conditionnel passé deuxième forme. (Bescherelle, Grammaire pour tous, §152)
