Unless otherwise specifically mentioned I have, in speaking of the sonata form, referred to it in connection with the pianoforte. But it also is the form employed for the symphony (which simply is a sonata for orchestra); for pianoforte trios, quartets and quintets; for string quartets and other branches of chamber music (which are sonatas written for the combination of instruments mentioned and such others as are employed in chamber music), and for concertos (which are sonatas for the combination of a solo instrument like the pianoforte, violin or violoncello, with orchestra). In these branches the sonata form has held its own more successfully than on the pianoforte, and for several extraneous reasons. In the symphony it is due largely to the greater variety that can be achieved through orchestral coloring; in chamber music largely to the somewhat super-refined and timorous taste of its devotees which would regard any startling innovation as highly indecorous; and in the concerto to the fact that a soloist who appears at an orchestral concert is supposed to play a concerto simply because the orchestra is there to play it with him, although he, as well as the audience, probably would find a group of solos far more effective. In fact I think that much of the applause which usually follows a great pianist's playing of a concerto is due not so much to the audience's enthusiasm over it as to the hope that he may be induced to come out and play something alone. So far as the symphony is concerned, it is liberating itself more and more from the sonata form and taking the direction indicated by Liszt in his symphonic poems and by Richard Strauss in his tone poems, the freest form of orchestral composition yet conceived.
In music, as in other arts, periods overlap. We have seen that during Bach's life Scarlatti in Italy was laying the foundations of the harmonic system and shaping the outlines of the sonata form which was to develop through Philipp Emanuel Bach, Haydn and Mozart and find its greatest master in Beethoven. Likewise, even while Beethoven was creating those works which are the glory of the classical period, two of his contemporaries, Carl Maria von Weber, who died one year before him, and Franz Schubert, who survived him by only a year, were writing music which was destined to turn the art into new channels. Weber (1786-1826) is indeed regarded as the founder of the romantic school through his opera "Der Freischütz." It seems to me, however, that Schubert (1797-1828) contributed quite as much to the new movement through his songs, while the contributions of both to the pianoforte are important. Weber was a finished pianist, had an enormous reach (he could stretch a twelfth), and besides utilizing the facility thus afforded him to add to the brilliancy of pianoforte technique (as in his well-known "Concert Piece for Piano and Orchestra"), he deliberately, in some of his compositions, ignored the sonata form and wrote a "Momento Capriccioso," a "Polonaise," a "Rondo Brilliant," a "Polacca Brilliant" and the fascinating "Invitation to the Dance." The last, even in its original form and without the elaborations in Tausig's version of it, and the "Concert Piece" still are brilliant and effective numbers in the modern pianoforte repertoire. Considering the age in which they were composed, their freedom from pedantry is little short of marvelous.