> The past tense is made to agree in gender with the subject, for it is the participle in an originally periphrastic perfect formed (like the perfect passive tense in Latin) with the present tense of the verb "to be" быть [bɨtʲ], which is now omitted except for rare archaic effect, usually in set phrases (откуда есть пошла земля русская [ɐtˈkudə jesʲtʲ pɐˈʂla zʲɪˈmlʲa ˈruskəjə], "whence is come the Russian land", the opening of the Primary Chronicle in modern spelling).
The participle nature of past-tense forms is exposed also in that they often have an extra suffix vowel, which is absent …