Rule reminder
Sequence of tenses (concordanza dei tempi) for the subjunctive: PRESENT/FUTURE main verb → present subjunctive (simultaneous/future) or present perfect subjunctive (past). PAST/CONDITIONAL main verb → imperfect subjunctive (simultaneous/future) or pluperfect subjunctive (past). Literary/formal Italian strictly observes these rules; colloquial Italian sometimes breaks them.
Era impossibile che nessuno _____ sentire quello sparo così forte.