Grimm's law
Schlegel was a promoter of the Romantic movement and inspired Samuel Taylor Coleridge, Adam Mickiewicz and Kazimierz Brodziński. The first to notice what became known as Grimm's law, Schlegel was a pioneer in Indo-European studies, comparative linguistics, and morphological typology, publishing in 1819 the first theory linking the Indo-Iranian and German languages under the Aryan group.