The past subjunctive is formed by using the subjunctive of the helping verb (avoir or être) + the past participle of the action being performed. The past subjunctive is used like the passé composé to express an action that has already taken place in the past: Il est regrettable qu'il n'ait pas réussi. (It is a shame that he didn't succeed.) Il est douteux qu'ils soient partis. (It is doubtful that they left.) Il est important qu'elles se soient bien amusées. (It is important that they had a very good time.)