Just as Johannes Brahms had done with his Opus 120, Reger also provided parts for two alternative solo instruments for his Sonata op. 107: I will also arrange the clarinet part for viola, so that the work can also be played thus (letter to his publisher). He by no means wanted to leave the arrangement of the viola part to the publisher, as slurs had to be changed here and there as well as octave transpositions had to be made - only I can do this work! The viola's sonorous mid range comes close to that of the clarinet, but lends the work its own timbre.