already hinted at the fact that there is an intimate
relationship between the compositions usually heard at a classical
concert. Symphonies, symphonic poems, concertos for solo instruments
and orchestra, as well as the various forms of chamber music, such as
trios, quartets, and quintets for strings, or pianoforte and strings,
are but different expressions of the idea which is best summed up in
the word sonata. What musicians call the "sonata form" lies at the
bottom of them all--even those which seem to consist of a single
piece, like the symphonic poem and overture. Provided it follow, not
of necessity slavishly, but in its general structure, a certain scheme
which was slowly developed by the geniuses who became the law-givers
of the art, a composite or cyclical composition (that is, one
composed of a number of parts, or movements) is, as the case may be, a
symphony, concerto, or sonata. It is a sonata if it be written for a
solo instrument like the pianoforte or organ, or for one like the
violin or clarinet, with pianoforte accompaniment. If the
accompaniment be written for orchestra, it is called a concerto. A
sonata written for an orchestra is a symphony. The nature of the
interpreting medium naturally determines the exposition of the form,
but all the essential attributes can be learned from a study of the
symphony, which because of the dignity and eloquence of its apparatus
admits of a wider scope than its allies, and must be accepted as the
highest type, not merely of the sonata, but of the instrumental art.
It will be necessary presently to point out the more important
modifications which compositions of this character have undergone in
the development of music, but the ends of clearness will be best
subserved if the study be conducted on fundamental lines.

[Sidenote: _What a symphony is._]

[Sidenote: _The bond of unity between the parts._]

The symphony then, as a rule, is a composition for orchestra made up
of four parts, or movements, which are not only related to each other
by a bond of sympathy established by the keys chosen but also by their
emotional contents. Without this higher bond the unity of the work
would be merely mechanical, like the unity accomplished by sameness of
key in the old-fashioned suite. (See Chapter VI.) The bond of
key-relationship, though no longer so obvious as once it was, is yet
readily discovered by a musician; the spiritual bond is more elusive,
and presents itself for re