[Illustration: Example 50. Fragment of Grieg.]
Comparing this sentence with Ex. 48, we discover the following significant difference: There, no more than two phrases were present; the whole sentence was reducible to two phrases. Here (Ex. 50), however, no such reduction is possible; three sufficiently similar—and sufficiently different—phrases are coherently connected, without evidence of mere repetition; it is the result of Addition, and the form is a phrase-group. The first cadence is, strictly speaking, a perfect one; but of that somewhat doubtful rhythmic character, which, in conjunction with other indications, may diminish its conclusive effect, and prevent the decided separation which usually attends the perfect cadence. This is apt to be the case with a perfect cadence so near the beginning (like this one) that the impression of "conclusion" is easily overcome. In a word, there is no doubt of the unbroken connection of these three phrases, despite the unusual weight of the first cadence. See also the first cadence in Ex. 51.
By simply continuing the process of addition (and avoiding a decisive perfect cadence) the phrase-group may be extended to more than three phrases, though this is not common.
THE DOUBLE-PERIOD.—A third method consists in expanding the period into a double-period (precisely as the phrase was lengthened into a double-phrase, or period), by avoiding a perfect cadence at the end of the second phrase, and adding another pair of phrases to balance the first pair. It thus embraces four coherent phrases, with a total length of sixteen measures (when regular and unextended).
An important feature of the double-period is that the second period usually resembles the first one very closely, at least in its first members. That is, the second phrase contrasts with the first; the third corroborates the first; and the fourth either resembles the second, or contrasts with all three preceding phrases. This is not always—though nearly always—the case.
The double-period in music finds its poetic analogy in almost any stanza of four fairly long lines, that being a design in which we expect unity of meaning throughout, the progressive evolution of one continuous thought, uniformity of metric structure (mostly in alternate lines), the corroboration of rhyme, and, at the same time, some degree and kind of contrast,—as in the following stanza of Tennyson's:
Phrase 1. "The splendor falls on castle walls,
Phrase 2. And snowy summits old in story;
Phrase 3. The long light shakes across the lakes,
Phrase 4. And the wild cataract leaps in glory."
The analogy is not complete; one is not likely to find, anywhere, absolute parallelism between music and poetry; but it is near enough to elucidate the musical purpose and character of the double-period. And it accounts for the very general choice of this form for the hymn-tune.
The following illustrates the double-period, in its most regular and convincing form (Beethoven, pianoforte sonata, op. 49, No. 1):—