THE PHRASE-GROUP.—A second method consists in enlarging the period-form to three phrases, by the same process of addition which, as explained in the preceding chapter, transforms the single phrase into the double-phrase or period. In order to preserve the continuity of the three phrases, it is evident that the second phrase must also close with a semicadence,—the perfect cadence being deferred until the last phrase is concluded.
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This form, be it well understood, does not include any of the triple-phrase designs which may result from merely repeating one or the other of the two phrases that make a period, as is shown in Ex. 48. All such phrase-clusters as are reducible to two phrases, because nothing more than simple repetition has been employed in their multiplication, should always be classed among ordinary periods; for two successive phrases, if connected (that is, unless they are purposely broken asunder by a definite perfect cadence at the end of the first phrase) always represent the analogy of Question and Answer.
The enlarged form we are at present considering consists of three different phrases, as a general rule; probably very closely related, or even distinctly resembling one another; but too independent, nevertheless, to constitute actual repetition, and therefore to admit of reduction to two phrases. For this very reason it cannot justly be called "period" at all, but takes the name of "phrase-group." An illustration by diagram will make the distinction clear:—
[Illustration: Phrase group diagram.]
Observe that the classification depends upon the number of phrases,—upon the melodic identity of the phrases,—and upon the quality of the cadences.
No. 1 is illustrated in Ex. 15; No. 2, in Ex. 42 and the first four measures of Ex. 43 (cadence not perfect, it is true, but same phrase-melody and same cadence); No. 3 is seen in Ex. 44 (phrase-melody similar, but cadences different)—also in Ex. 47; No. 4 is seen in Ex. 48; No. 5 is rare, but an example will be discovered in Lesson 8; No. 6 is illustrated in the following (Grieg, op. 38, No. 2):—