Ukrainian (українська мова, ukrainska mova, IPA: [ʊkrɐˈjinʲsʲkɐ ˈmɔwɐ]) is an East Slavic language, spoken primarily in Ukraine. It is the first (native) language of a large majority of Ukrainians. Written Ukrainian uses the Ukrainian alphabet, a variant of the Cyrillic script. The standard language is studied by the National Academy of Sciences of Ukraine and Potebnia Institute of Linguistics. Comparisons are often made between Ukrainian and Russian, another East Slavic language, yet there is more mutual intelligibility with Belarusian, and a closer lexical distance to West Slavic Polish and South Slavic Bulgarian. Ukrainian is a descendant of Old East Slavic, a language spoken in the medieval state of Kievan Rusʹ. In the Grand Duchy of Lithuania, the language developed into Ruthenian, where it became an official language, before a process of Polonization began in the Polish–Lithuanian Commonwealth. By the 18th century, Ruthenian diverged into regional variants, and the modern Ukrainian language developed in the territory of present-day Ukraine. Russification saw the Ukrainian language banned as a subject from schools and as a language of instruction in the Russian Empire, and continued in various ways in the Soviet Union. Even so, the language continued to see use throughout the country, and remained particularly strong in Western Ukraine.