The pluperfect subjunctive
The pluperfect subjunctive, as you might expect, is formed from the past subjunctive form of avoir or être along with the past participle. So, for example, the pluperfect subjunctive form of manger would be eût mangé; the pluperfect subjunctive form of venir would be fût venu.
It should be borne in mind that, like the past subjunctive, the pluperfect subjunctive is becoming less and less used. When it carries a strictly pluperfect value, the pluperfect subjunctive is often replaced in current usage by the perfect subjunctive (or in speech, the ordinary pluperfect indicative is sometimes possible), so that of the following forms:
form (c) is typical only of very formal usage; in most kinds of day-to-day speech, (a) would tend to be preferred, or else (b), and in writing, where (a) might be considered unacceptable, (b) would often be an acceptable substitute.
Written by Neil Coffey.