The next logical step is for the composer to invent his own imitation of a folk melody, then to treat it exactly like the borrowed tune. To Bartók it made no difference whether the composer invented his own themes or borrowed material. He stated emphatically that the composer "has a right to use musical material from all sources. What he has judged suitable for his purpose has become through the very use his mental property…. The question of origins can only be interesting from the point of view of musical documentation."
The highest form of folk-influenced music, Bartók believed, is that in which the folk atmosphere has been completely assimilated. He described such music as follows: "Neither peasant music nor imitations of peasant melodies can be found in his [the composer's] music, but it is pervaded by the atmosphere of peasant music. In this case we may say he has completely absorbed the idiom of peasant music which has become his musical mother tongue." No better description could be given of the part played by folk music in Bartók's mature work.