Ukrainian (украї́нська мо́ва ukrayins'ka mova, pronounced [ukrɑˈjɪɲsʲkɑ ˈmɔwɑ]) is a member of the East Slavic subgroup of the Slavic languages. It is the official state language of Ukraine and the principal language of the Ukrainians. Written Ukrainian uses a variant of the Cyrillic script.
The Ukrainian language traces its origins to the Old East Slavic of the early medieval state of Kievan Rus'. From 1804 until the Russian Revolution Ukrainian was banned from schools in the Russian Empire of which Ukraine was a part at the time. It has always maintained a sufficient base in Western Ukraine where the language was never banned in its folklore songs, itinerant musicians, and prominent authors.
The standard Ukrainian language is regulated by the National Academy of Sciences of Ukraine (NANU), particularly by its Institute for the Ukrainian Language, Ukrainian language-informatical fund, and Potebnya Institute of Language Studies. Ukrainian, Russian, Belarusian, and Rusyn have a high degree of mutual intelligibility. Lexically, the closest to Ukrainian is Belarusian (84% of common vocabulary), followed by Polish (70%), Serbo-Croatian (68%), Slovak (66%) and Russian (62%).
A point of view developed during the 19th and 20th centuries by linguists of Imperial Russia and the Soviet Union. Like Lomonosov, they assumed the existence of a common language spoken by East Slavs in the past. But unlike Mikhail Lomonosov's hypothesis, this theory does not view Polonization or any other external influence as the main driving force that led to the formation of three different languages: Russian, Ukrainian and Belarusian from the common Old East Slavic language.
Soviet scholars set the divergence between Ukrainian and Russian only at later time periods (14th through 16th centuries). According to this view, Old East Slavic diverged into Belarusian and Ukrainian to the west (collectively, the Ruthenian language of the 15th to 18th centuries), and Old Russian to the north-east, after the political boundaries of Kievan Rus' were redrawn in the 14th century. During the time of the incorporation of Ruthenia (Ukraine and Belarus) into the Polish–Lithuanian Commonwealth, Ukrainian and Belarusian diverged into identifiably separate languages.