The status of the Ruthenian language and use of Lithuanian in public life in the Grand Duchy of Lithuania (henceforth GDL) remains one of the most hotly debated topics in Lithuanian historiography. In this article, the use of Ruthenian (early Belarusian) is analysed as the official (‘state’) language of the GDL, as it is presented in the latest works by Belarusian and Polish researchers and Lithuanian language studies researchers. This analysis looks at the problems that arise when examining the flexible and extraordinarily dynamic use and interrelation of languages in the GDL in the 15th–16th centuries, which changed every few decades and was based more on customs and traditions than laws.

The status of the Ruthenian language and use of Lithuanian in public life in the Grand Duchy of Lithuania (henceforth GDL) remains one of the most hotly debated topics in Lithuanian historiography. In this article, the use of Ruthenian (early Belarusian) is analysed as the official (‘state’) language of the GDL, as it is presented in the latest works by Belarusian and Polish researchers and Lithuanian language studies researchers. This analysis looks at the problems that arise when examining the flexible and extraordinarily dynamic use and interrelation of languages in the GDL in the 15th–16th centuries, which changed every few decades and was based more on customs and traditions than laws.