Chapter 24

_the reproduction of Part I_, and therewith the fulfilment of the important principle of return and confirmation. The reproduction is sometimes exact and complete; sometimes slight changes, or even striking variations, possibly certain radical alterations, occur; sometimes it is only a partial recurrence, the first few measures being sufficient to prove the "Return"; sometimes, on the other hand, considerable material (more or less related) is added, so that Part III is longer than the First Part.

From this it appears that much latitude is given to the composer, in his formulation of the Third Part. All that the Part has to prove, is its identity as confirmation of the leading motive, and this it may do in many ways, and with great freedom of detail, without obscuring the main purpose. It is precisely this richness of opportunity, this freedom of detail, which enhances the beauty and value of the tripartite forms.

The following is a very regular example of the Three-Part Song-form (Schumann, op. 68, No. 20):--

This version is as complete as it can conveniently be made upon one single staff (chosen in order to economize space); but the student will find the formal design somewhat more plastically defined in the original, complete form, and he is therefore expected to refer to the latter. Part I is an unusually regular double-period, with three semicadences and a strong perfect cadence, on the original tonic, to mark its conclusion; the double-bar is an additional confirmation of the end of the Part. The second Part runs in the key of E major (the dominant of the original key) throughout; its form is only a phrase, but repeated,--as is proven by the almost literal agreement of the second phrase with the preceding one, _cadence and all_. Part III agrees literally with Part I in its melodic formation, but differs a little in the treatment of the lower (accompanying) voices.

In the theme of Mendelssohn's pianoforte Variations in E-flat major (op. 82), which see, the design is as follows:--Part I is a period of eight measures. Part II is also an 8-measure period, ending upon the tonic chord of B-flat major (the dominant key), as first eighth-note of the 16th measure; the following eighth-note, b-natural, represents what we have called the Retransition (in its smallest conceivable form), as it fulfils no other purpose than that of leading back into the first tone of the First Part. Part III is _only a phrase_, and therefore shorter than Part I; but it corroborates the _beginning_, and, in fact, the entire contents of the First Part.

The plan of Mendelssohn's 28th Song Without Words is as follows:--First number the 38 measures, _carefully_. The first four measures are an introductory phrase, or prélude; Part I begins in the second half of measure 4 (after the double-bar) and extends, as regular 8-measure period, to measure 12. Part II follows, during the same measure; its form is a period, extending to measure 20, and closing with a very distinctly marked semicadence on the dominant chord (chord of D). Part III is 14 measures long, containing therefore six more measures than the First Part; its first phrase is almost exactly like the first phrase of Part I; its second phrase (measures 25-28) differs from any portion of Part I, but closely resembles the melodic formation of Part II; its third phrase is based upon the preceding one (_not_ as repetition, however), and is expanded to the 34th measure. The form of