When the introductory passage is longer than three measures, it probably constitutes a complete phrase by itself, with its own cadence; in which case, of course, it must not be analyzed as "extension." For example, at the beginning of No. 29; still more apparently at the beginning of No. 28, No. 41, and others.
INHERENT IRREGULARITY.—Finally,—there exists another, third, condition, besides those mentioned at the head of this chapter, whereby a phrase may assume an irregular dimension; not by doubling or dividing its length (as in the large and small phrases) nor by the processes of extension,—but by an arbitrary and apparently incalculable act of melodic liberty,—by allowing the melody to choose its own time for the cadential interruption. This comparatively rare occurrence is illustrated in Ex. 17, No. 1 (five-measure phrase), and Ex. 17, No. 2, second phrase (six measures long). It is true that in each of these cases the "extra" measures might be accounted for as "extension by modified repetition,"—for instance, in No. 1 the second measure might be called a reproduction (or extension) of the first measure. But cases will be encountered where a phrase of three, five, six, or seven measures will admit of no such analysis. In such instances the student is compelled to rely simply upon the evidence of the cadence. As was advised in the context of Ex. 17, he must endeavor to define the phrase by recognition of its "beginning" and "ending," as such; or by exercising his judgment of the "cadential impression." See also Ex. 48, second phrase (six measures).
See Schubert, pianoforte sonata No. 1 (A minor, op. 42) Scherzo-movement; first 28 measures, divided into 5 phrases,—as demonstrated by the melodic formation—of 5, 5, 5, 7 and 6 measures. Also Schubert, Impromptu, op. 90, No. 3, measures 42 to 55 (phrases of 5, 5 and 4 measures.)
LESSON 6. Analyze the following examples, locating the cadences and defining their value (as perfect or semicadence); and determining the nature of each irregular phrase (as small, large, or extended phrase):
Beethoven, pianoforte sonata, op. 22, second movement (Adagio), first 30 measures.
Beethoven, pianoforte sonata, op. 28, Scherzo-movement.
Beethoven, pianoforte sonata, op. 14, No. 3, Menuetto.
Mendelssohn, Songs Without Words: No. 4, first 5 measures.
No. 46, last 9 1/2 measures.