AMONG the many valuable contributions of William Dwight Whitney to linguistic science is one especially important and fundamental principle. It may be stated in these words. In explaining the prehistoric phenomena of language we must assume no other factors than those which we are able to observe and estimate in the historical period of language development. The factors that produced changes in human speech five thousand or ten thousand years ago cannot have been essentially different from those which are now operating to transform living languages. On the basis of this principle we look to-day at a much-discussed problem of Indo-European philology with views very different from the views held by the founders of Comparative Philology and their immediate successors. I refer to the problem, how the Indo-European people came to assign gender to nouns, to distinguish between masculine, feminine, and neuter. This question is of interest to others besides philologists. What man of culture who has learned languages such as the Greek, Latin, or French has not at times wondered that objects which have no possible connection with the natural gender of animals appear constantly in the language as male or female? In German, for example, it is der fuss, but die hand; der geist, but die seele; in Latin, hīc hortus, hīc animus, hīc amor, but haec planta, haec anima, haec felicitas; in Greek, ὁ πλοῦτος, ὁ οἶκος, but ἡ πενία, ἡ οἰκία.

This gender distinction pervades all the older 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 illustrate 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.