 The ancient aorist, imperfect, and (periphrastic) pluperfect have been lost.The loss of three of the former six tenses has been offset by the reliance, as in other Slavic languages, on verbal aspect.Most verbs come in pairs, one with imperfective or continuous connotation, the other with perfective or completed, usually formed with a (prepositional) prefix, but occasionally using a different root.