Some Germanic verb forms often known as subjunctives are actually descendants of the Proto-Indo-European optative. Primary subjunctives are changed to the corresponding secondary subjunctives, which stay the same. The truth of subjunctives of freedom cannot be discerned a priori, for they are contingent. Despite their English names, both German subjunctives can be used for past and present time. Subjunctives occur most often, although not exclusively, in subordinate clauses, particularly "that"-clauses.