The Latvian linguist Jānis Endzelīns thought, however, that any similarities among Baltic and Slavic languages resulted from intensive language contact, i.e. that they were not genetically more closely related and that there was no common Proto-Balto-Slavic language.
Den lettiske sprogforsker Jānis Endzelīns mente imidlertid, at eventuelle ligheder mellem baltiske og slaviske sprog havde udviklet sig som resultat af intensiv sproglig kontakt, dvs. at de ikke var havde fælles ophav, og at der ikke var noget fælles Proto-Balto-slaviske sprog.