n the
sentence has been completed by the sense and not necessarily by the
period which is placed after the last word.

There are a few leading types of form to which all others more or less
conform. The first of these, and perhaps, on the whole, the most
important, are those which are called unitary forms. A unitary form is
a musical form with only one leading melodic idea, out of which the
entire piece is developed. This can only be done in one or the other
of three ways. Taking the simplest way first, it will be to develop
this leading idea into a song form according to the pattern given
above, in the beginning of this discussion. This, being sufficiently
obvious on the face of it, requires no further attention here. Forms
of this kind belong essentially to popular music, although they are not
uncommon by way of relief in the more elevated art music.

There are two types of unitary form, however, which enter into and
color all instrumental music to a degree, making it indispensable that
the pupil thoroughly understand them. The first of these is the fugue.
In the fugue a melodic subject of two measures or four, rarely more, is
taken by a single voice and is answered by another voice in the
dominant, and this again by the third voice in the original key, and so
on according to the number of voices performing the fugue. The voice
which has completed the subject goes on with the counter-subject or the
counterpoint while the second voice is singing the subject. When all
the voices have had their turn at the phrase there is an interlude of
modulating material, after which the subject comes again and is
answered one or more times in the properly related keys, for which the
artificer of fugues has his rules already prepared, following the
principles laid down by Bach. After this second appearance of the
theme in these new keys, another interlude, and then an additional
strophe in still a different key and with finer treatment; and thus,
according to the fancy of the composer and his skill, the piece is
extended to one, two, or even six or eight pages. But during the whole
of it the principal subject has reappeared at very short intervals and
in a great variety of keys, while the interlude matter has always been
of a lighter and less significant character. In order to arrive at an
appreciation of fugues, the student perhaps can not do better than to
begin with some of the two-part inventions of Bach, which, while