The traditional division between "original" and "arrangement" is impossible to sustain for most of Liszt's oeuvre. By virtue of the amount of original creative thinking displayed in his finest operatic fantasies and transcriptions they deserve as detailed a study as any other group of works. Our knowledge is deficient even with regard to identification and dating; the Fantasia on Le Nozze di Figaro and Don Juan is unknown in its original form, while the Fantasia on Il Giuramento has remained unidentified. All of Liszt's works share the same improvisatory approach to composition. Both original and operatic themes are found in his sketchbooks, although sketches of larger sections of the fantasias are rare. Many operatic pieces originated hi concert-improvisations before being committed to paper. Thereafter they were subjected to a process of revision that frequently continued after publication. The operatic fantasias of the 1830's and 40's illustrate Liszt's episodic treatment of musical form, with an indulgence in short-range harmonic effects and little concern for overall tonal planning. Some techniques of thematic metamorphosis and transition anticipate features of Liszt's Weimar compositions, and the roots of his fondness for concluding apotheoses can be clearly seen, particularly in the Fantasia on Der Freischütz. The fantasias and transcriptions vividly illustrate the course of Liszt's compositional and pianistic development, from early precocity through mature mastery to late austerity. The influence of Thalberg can be detected as the motivation for Liszt's return to the operatic fantasia after a hiatus of several years, although he did not adopt aspects of Thalberg's piano style until 1839. His finest fantasias from the years 1839-43 are characterised by bold virtuosity, compositional ingenuity and a striking attempt to encapsulate the dramatic course of an opera within the confines of a fantasia. As operatic pieces formed a large part of Liszt's concert repertoire until 1848 they were almost invariably based on operas of proven popularity. A more innovative and altruistic choice of material is evident only from the beginning of the Weimar period.