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