The chord of the sixth on the seventh of the major scale, may descend diatonically on the common chord of the re lative minor and then it forms an inversion of the inter , rupted cadence; Ex. 12. which is the beginning of a beau tiful duet of Mozart, only transposed into the key of C; in which the other examples are written.
When a common chord descends a third to a chord of the sixth, the fundamental progression is the descent of a fifth to another common chord; and when a chord of a sixth rises one degree to a common chord, the fundamental pro gression is the ascent of fourth from one common chord to another. Ex. 13. is therefore the same fundamental pro gression as Nos. 1, 2, 3. in art. 110; which is pointed out by the dots under each chord of the sixth. Ex. 14. is the sante fundamental progression as Nos. 6, and 7. in art. 110; as shown by the dots under each chord. Ex. 13. is the sante fundamental progression, consisting entirely of chords of the sixth.
The common chord is succeeded by a chord of the sixth, on the same bass, in a very agreeable manner; and when the bass of this second chord rises diatonically to a new common chord, which is again succeeded by a chord of the sixth on the same bass, the progression forms what is called a sequence of fifths and sixths. Ex. 16. is written in four parts; by leaving ont the third part next the bass, which consists of the octave and doubled sixth alternately, we have the sequence in three parts, in which form it more frequently appears. This is a very beautiful and effective progression, much in use by the first masters.
Chords of the sixth are used with far greater freedom than the common chords from which they are derived. A series of common chords ascending or descending diatonically in similar motion of the parts, would be quite intolerable. Yet this is a treatment which chords of the sixth frequently re ceive from the best composers. Nos. 17 and 18 are exam ples of such sequences of sixes ascending and descending. The reader will observe, that between the first and second parts there is a continual succession of perfect fourths ; but the bass part at the distance of a third from the lower, so corers the fourths, that the succession gives no offence. Yet the same succession of fourths without the bass, or naked, would be as offensive as so many perfect fifths. Utile ba.ss
be removed an octave loWer, at a distance of tenth from the other part, the effect of the series of fourths becomes more observable, insomuch that Mr. Kollmann absolutely prohibits it. However, WC shall find examples of a series of sixes, where the bass is at the distance of tenth from the second part, in good authors. The reinoval of the second part an octave higher, to alter the position of the chords, would produce a series of perfect fifths. The form here given is therefore the only one in which this sequence can take place. In these two examples, the sixth on the second of the major scale, in which the fourth is major, is treated as a discord: but this is done merely for the sake of a kind of termination; for this sixth is in such sequences used as freely as the others, its dissonant nature being, from the re gularity of the succession, overlocg(ed.
The bass may be doubled in the octave below; or four rcal parts may be had by putting the bass an octave lower, and lakinfr to it an 8th and doubled Gth alternately, as in No. 19. This example is taken from Shield's Introduction to IIarmony; and we shall quote the observations with which this excellent author accompanies it. " The bitter cries of naked fourths are so shockinn. to the ears of a feel ing composer, that Ire never suffers tIlern to remain long in any situation without clothing : How disagreeably this group (of fourths in the two upper parts) howl without their asso ciate! But how pleasantly they sing in four parts, when Ire and his companion the eighth join them !" that is, the sixth and eighth reckoned downwards from the highest note. In this example, the reader will observe that the-dissonant sixth, on the fourth of the minor scale, is here avoided by flattening the E : but he will find the effect still very good, by- playing E natural instead of it. The student may also observe the manner in which the accidental flat and sharp are signified in the figures of the bass; by the b 6, and by the 0: the dash through the last signifying that the sixth is to be taken semi tone higher than the minor scale of D would give it.