Indo-european languages, and must therefore be regarded as having its origin in the time of the pro-ethnic indo-european community. Not only is the subject itself full of interest, but also the treatment it has received from the philological research of our century. The various efforts made to solve the problem may very aptly illus trate an essential difference which exists between the theories of language development held in the beginning and middle of this century and those which prevail to-day, — a difference of method existing not in comparative linguistics alone, but also in other fields of philological and historical research that border on it.