Imperfect and Pluperfect Subjunctive
Although these tenses are not used in speaking, it is possible that they will appear in literature.
The imperfect subjunctive is formed by dropping the final letter of the je form of the passé simple and adding the endings shown in Table 1.
The pluperfect subjunctive is formed by combining the imperfect subjunctive of the helping verb ( avoir [ eusse, eusses, eût, eussions, eussiez, eussent]) or être [ fusse, fusses, fût, fussions, fussiez, fussent]) + the past participle of the verb denoting the action. The pluperfect subjunctive is used in literature only when the main clause is in any other time but the present:
Je ne croyais pas qu'il fût revenu. (I didn't think he had come back.)