The word Part (written always with a capital in these lessons) denotes, then, one of these larger sections. The design of the Part-forms was so characteristic of the early German lied, and is so common in the song of all eras, that the term "Song-form" seems a peculiarly appropriate designation, irrespective of the vocal or instrumental character of the composition.
The student will perceive that it is the smallest class of forms—the Phrase-forms,—embracing the phrase, period and double-period, to which the preceding chapters have been devoted. These are the designs which, as a general rule, contain only one decisive perfect cadence, and that at the end; and which, therefore, though interrupted by semicadences, are continuous and coherent, because the semicadence merely interrupts, and does not sever, the continuity of the sentence. (This grade of forms might be called One-Part forms).
THE PARTS.—If we inquire into the means employed, in the larger Part-forms, to effect the division of the whole into its broader Parts, we find that the prime factors, here again, are Cadence and Melody. The strongest sign of the consummation of a Part is a decisive perfect cadence, resting, as usual, upon the tonic harmony of the chosen key; a cadence sufficiently emphatic to interrupt the closer cohesion of the phrases which, precede, and bring them, as completed Part, to a conclusion. Such a cadence, marking the end of the First Part, may be verified in Mendelssohn's Songs Without Words, No. 23, measure 15; No. 3, measure 29 (at the double-bar,—a sign which frequently appears at the termination of Part One); No. 20, measure 21; No. 27, measure 12; No. 34, measure 10.
Another indication of the Part-form is a palpable change in melodic character in passing from one Part into the next; sufficient to denote a more striking "new beginning" than marks the announcement of a new phrase only. The change, however, is as a rule not very marked; it is sometimes, in fact, so slight as to be no more than simply palpable, though scarcely definable on the page. For these divisions are, after all, the several "Parts" of one and the same song-form, and, therefore, any such radical change in melodic or rhythmic character, or in general style, as would make each Part appear to be a wholly independent musical idea (subject or theme), would be manifestly inconsistent.
Generally, both these factors (cadence and melody) unite to define the end of one Part and the beginning of the next. Should either one be feeble, or absent, the other factor will be all the more pronounced. Thus, the cadence of Part One may be less decisive, if the change in melodic character at the beginning of Part Two is well marked; this is seen in No. 33, measure 12. The reverse—a strong cadence and but little melodic change,—in No. 13, measure 20.
THE FIRST PART.—Part One may be designed as period, double-period, or phrase-group; sometimes, though very rarely, as single phrase, repeated. It ends, usually, with a strong perfect cadence on the tonic chord of the original key, or of some related key (that is, one whose signature closely resembles that of the original key). An introductory phrase, or independent prelude, may precede it.
THE SECOND PART.—Part Two, as intimated, is likely to begin with a more or less palpable change of melodic character,—by no means is this always the case. It may be designed, also, as period, double-period, or phrase-group, and is somewhat likely to be a little longer (more extended) than Part One. A concluding section (called codetta if small, coda if more elaborate) often follows, after a decided perfect cadence in the original key has definitely concluded the Part.
The following is one of the simplest examples of the Two-Part Song-form (a German lied by Silcher):—
