This thesis is concerned with the guitar music of Nathanael Diesel. The music is contained in two manuscript collections, Ny Kgl. Saml. 110, and Gl. Kgl. Saml. 377. This study has centered on the duets for guitar of which there are ninety-six movements. Sixty-five of these are to be found in twelve suites. The remaining music in the collections is for guitar solo. This is the largest collection of music known for two guitars and various combinations of instruments with guitar. Its uniqueness is only surpassed by its quality. This study has shown that Nathanael Diesel must be considered an important link between the Baroque and the Classical period because of his advanced compositional technique for the guitar. In many of the works he shows a very definite tendency toward writing with an Italianate melodic style, one which does not appear in the works of his contemporaries.
The elements which he employs in constructing melodies are note repetition, sequence, echo effects and figuration. Also a large proportion of the duets are written in the ABA form (37) whereas his lutenist contemporaries used mainly the AB form. Within these duets twenty different dance forms can be found from the allemanda to the sarabanda and free style single-section movements from allegro to vivace. Diesel is somewhat conservative with regard to the use of a variety of tonalities, the most common being C, F, d-minor and a-minor. With regard to modulation, he departs from the usual in that while employing many cadences on the dominant, he most often modulates to the relative key, a practice not seen among his contemporaries whether lutenist or guitarist. Diesel presents another unique aspect of the Baroque guitar and that is that for the first time a composer employs the low A tuning on the fifth string. The usual, as we have seen, is the re-entrant tuning as used by de Visee and Corbetta. His use of the technical possibilities of the guitar is limited, and he rarely ventures beyond the first position.