Silesian or Upper Silesian is a West Slavic ethnolect of the Lechitic group spoken by a small percentage of people in Upper Silesia. Its vocabulary was significantly influenced by Central German due to the existence of numerous Silesian German speakers in the area prior to World War II and after. Some regard it as one of the four major dialects of Polish, while others classify it as a separate regional language, distinct from Polish. The first mentions of Silesian as a distinct lect date back to the 16th century, and the first literature with Silesian characteristics to the 17th century.
Silesian speakers currently live in the region of Upper Silesia, which is split between southwestern Poland and the northeastern Czech Republic. At present Silesian is commonly spoken in the area between the historical border of Silesia on the east and a line from Syców to Prudnik on the west as well as in the Rawicz area.
Until 1945, Silesian was also spoken in enclaves in Lower Silesia, where the majority population spoke Lower Silesian, a variety of Central German. The German-speaking populace was either evacuated en masse by German forces towards the end of the war or deported by the new administration upon the Polish annexation of Silesia after World War II. Before the war, most Slavic speakers also spoke German and, at least in eastern Upper Silesia, many German-speakers were acquainted with Slavic Silesian.
According to the last official census in Poland in 2021, about 460,000 people declared Silesian as their native language (in census 2011, about 510,000), and in the censuses in Poland, Czech Republic and Slovakia, nearly 0.9 million people declared Silesian nationality (Upper Silesia has almost 5 million inhabitants, practically the vast majority in the Polish part of Upper Silesia speak Polish and Czech in the Czech part and declare themselves as Poles in the Polish part and Czechs in the Czech part.).
Although the morphological differences between Silesian and Polish have been researched extensively, other grammatical differences have not been studied in depth.