But still, Belorussian remains to be the closest tongue to Russian and represents a purely East Slavic language with all its flexions, the case system, and verb structure. Belorussian lost vocative case, lost dual number, aorist and perfect tenses. Three tenses that remain in the language are present, past and future. Two aspects, imperfective and perfective, verbal adverbs and participles, declinable adjectives and pronouns: all that is common with East Slavic languages.
As for phonetic system, Belorussian borrowed from Polish deep sibilants and extensive use of [ts] sound instead of Russian soft [t']. The open [e] in the former Slavic berjoza (a birch) is now pronounced as in Lithuanian or Polish like b'arjoza. The soft [d'] was converted to [dz] in Belorussian.