Investigations into any music require two supplementary and interdependent orders: the systematic order (of quality and quantity) and the historical order in time and space (contact and continuity). This basic truth has not always been realized. It is the systematic musical knowledge which from antiquity has been prevailing in Europe. The turning point took place only in recent times. In the last centuries European historism had dominated the scholarship of music. An illustration of the domination of history and its theoretical consequences is the classification of musical science by Guido Adler. Its characteristic feature is a division of music into two parts: one treated historically (classical music) and one treated systematically (Vergleichende Musikwissenschaft), as if any music could be studied without consideration of these two perspectives. Much has changed since Adler's classification and two opposing trends have emerged. The stronger of the two has expressed itself in an expansion of history. We can see this in the tendency to stress the historical aspect in ethnomusicology. Conversely, historians of music are now increasingly concerned with the folk music of various periods and stress its role in culture. This trend towards an historical approach in ethnomusicology can be seen in the work of various scholars and has also found its expression in the activities of the ICTM study group, set up to investigate historical sources of folk music. This study group was initiated by Walter Wiora and organized by Benjamin Rajeczky and Wolfgang Suppan. The group's efforts led to the two separate publications with the joint title “Historiche Volksmusikforschung”. In a way, this isolates and accentuates a new specialization within ethnomusicology.