 He was one of the first to describe the evolution from Old Norse to Modern Norwegian.From this he moved to advocate and design a distinctly Norwegian written language he termed "Landsmål", "language of the country".His work was based on two important principles, in morphology he chose forms which he regarded as common denominators from which contemporary varieties could be inferred, in lexicography he applied puristic principles and excluded words of Danish or Middle Low German descent when at least some dialects had preserved synonyms inherited from Old Norse.