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.