(often called _song-form_ or
_Lied-form_) consists of two periods so placed that the second
constitutes a consequent or antithesis to the first. The second half of
this second period is often exactly the same as the second half of the
first period, thus binding the two periods together into absolute unity.
The theme of the choral movement of the Ninth Symphony (Beethoven)
quoted below is a perfect example of this form. Other examples are
"Drink to Me Only With Thine Eyes," and "The Last Rose of Summer."

[Illustration: BEETHOVEN]

The _small three-part primary form_ is like the two-part primary form
except that it has a section of contrasting material interpolated
between the two periods. This middle part is usually an eight-measure
phrase.

The _large two- and three-part primary forms_ usually have
sixteen-measure periods instead of eight-measure ones, but are otherwise
similar in construction.

These various _primary forms_ are used in constructing many
varieties of compositions, among them the _theme and
variations_, the _polka_, the _waltz_, the _march_, etc., as
well as most of the shorter movements in sonatas, quartets,
etc. They are used in vocal music also, but are less apt to be
regular here because the form of vocal music is largely
dependent upon the structure of the text.

147. A _theme_ is a fragment of melody used as the subject of a fugue,
as the basis of the development section in "sonata form," etc. Sometimes
it is a complete tune (often in period form), on which variations are
made, as _e.g._, in the familiar _theme and variations_.

148. _Thematic development_ consists in taking a short theme (or several
short themes) and by means of transposition, interval expansion and
contraction, rhythmic augmentation and diminution, inversion, tonality
changes, etc., building out of it a lengthy composition or section of a
composition. Fig. 60 _b_, _c_, _d_, _e_, and _f_ show how the theme
given in Fig. 60 (_a_) may be varied in a few of these ways. There are
hundreds of other fashions in which this same theme might be varied
without destroying its identity. For other examples of thematic
development see the development section of Sonata Op. 31, No. 3, as
analyzed in Appendix E. [Transcriber's Note: Corrected error "Sec. 3" in
original.]

[Illustration: Fig. 60.]

For further illustrations of development in the case of this
same theme, see--Christiani--The P