form also lies at the foundation of
the great majority of salon pieces for the piano.

The only difference between the rondo form and the form last
described--the proper designation of which is "song form with trio"--is
that the rondo introduces passage work between the subject and the
second subject. Should it be desired to develop the rondo to a greater
length, the second subject can be repeated after the repetition of the
first, and the first subject brought in still again. A third subject
can be introduced, and in the longest rondo form the schedule is like
this, C standing for the third subject:

A-B-A-C-A-B-A-Coda.

A form of this sort might extend to a very considerable length, as
happens in the case of Chopin's Rondo in E-flat major, opus 18, which
reaches to ten or twelve pages and occupies about ten minutes to
perform.

The essential principle of musical form--form in music--is quite
analogous to form in literature. As in a poem or article the first
consideration is Unity, or the preponderance of a leading idea, and the
second Variety, or the occurrence of interesting illustrative matter,
and the third Symmetry, or the just relation between the different
parts in order that the leading idea may not be obscured by the
prolixity of the subordinate ideas, so the same principles prevail in
music. Unity also is attained by peculiarly similar means in both
cases. As in the article the leading idea is repeated a number of
times in order to impress it upon the hearer, but frequently in
different language, so in music the principal idea is repeated more
times than any other in the course of the piece; and in the small
forms, or rather in the molecular construction of a piece of music, the
repetitions are in a great variety of speech, exactly as they are in a
well-made article. The same idea can be presented in different
aspects, and different words may express it. In music this takes place
through the appearance of the motive in different chords from those in
which it first appeared, giving rise to variations in the melodic
intervals and the like.

Symmetry in music is much more exactly observed than in literary
composition, even in verse, since music itself is a matter of time and
vibration, and the proportionate and mathematical relation of parts
belongs to the very essence of the art. Every musical form, therefore,
whether large or small, consists essentially of one leading idea and of
two or more