115. A chord of the sixth, like the common chords from which it is derived, has only three real parts. In composi tions of four parts it is more usual to double the sixth (which is the fundamental sound) or the third, (the fifth of the origi nal chord) than to take the octave to the bass. This rule, however, is by no means absolute, as Dr. Callcott might lead the readers of ltis Musical Grammar to think, except in a particular case, which we shall notice bye and bye. In par ticular, it must yield to that of avoiding consecutive perfect concords between the sante parts, as the following example from Mr. Shield will show.
The last chord in each of these examples is a discord, with which our readers have not yet been made acquainted. In the second example, the student will notice the fifths be tween the second and third parts, which, in the first exam ple are avoided by taking the octave to the bass of the first chord, instead of doubling the sixth. Like the common chord, the chord of the sixth ha.: different positions, and the harmony may be close or dispersed, as in the next examples.
Those positions are the best, in which the harmony is most equally dispersed. Those in which it is very une qually separated, as those marked with a cross, are not so agreeable, though cases will occur in which they may be used.
116. The chord of the sixth on the third of the key, or the first derivative of the tonic harmony, alternates very agree ably with the dominant chord. Ex. 1 and 2.
The chord of the sixth again on the major seventh of the scale or sensible note, which is the first inversion of the do minant chord, alternates very naturally with the common chord of the key, Nos. 3 and 4. The latter of these pro gressions, viz. from the first inversion of the dominant to the chord of the key, when it takes place on the proper part of the measure, forms an inverted cadence, by which musical phrases are frequently terminated in the middle of a strain. This is the case in which the octave to the bass of the 6th ought not to be taken; because the sensible note must rise diatonically to the key, and therefore must not be doubled.
The chord of the sixth on the second of the key is the first inversion of the imperfect common chord. This chord alternates very agreeably either with the chord of the key, or with its first derivative, Nos. 5, 6, 7. In the progression of this chord of the 6th to the harmony of the key, it receives that peculiar treatment which is called the resolution of a discord. The dissonant interval is the lesser fifth, or (as it appears in these examples front the position of the chord) the greater fourth from F to B. The B rises to C, and the
F falls to E: hence it is, that in Ex. 5 and 6, the second and third parts meet in unison; because to avoid consecu tive octaves between the bass and third part, this latter also rises to E.
The 6th in this chord is the sensible note, and the harmony of the key follows it as a matter of course. This is therefore really a dominant chord as decidedly as the common chord of the fifth of the key. We shall afterwards find these two chords, viz. the common chord of the fifth of the key, and the imperfect common chord of the major seventh, or sensi ble note, united, form what is called the dominant seventh. fn examples 8 and 9, the progressions of this chord of the sixth are exhibited in the minor mode, where the student -will observe that the sixth is accidentally sharpened that it may lie major, which is intimated in the fig-uring by the dash through the figure, thus 0; and thus the chord of the sixth on the second of the minor scale becomes similar to that of the major scale, and receives exactly the same treatment. This major sixth being the sensible note, ought never to be doubled. But wften this chord of the sixth is treated without regard to its dissonant nature, as in some of the following examples, the sixth may be doubled.
When the fourth of the key in the bass rises to the fifth of the key as leading chord, it is more agreeable and more usual to give the former a chord of the sixth, than a common chord; Ex. 10. This chord of the sixth, on the fourth of the key, is the first inversion of the common chord of the second of the scale; yet the harmony in this progression is felt as belongino. to the subdominant. 1Ve shall afterwards see that the staidominant may have its proper fifth along with this sixth, and that the whole subdominant chord thus formed, is made up of the common chords of the fourth and of the second of the scale united. In the minor mode this chord of the sixth on the subdominant, is the same inversion of the imperfect common cltord, which, in the major mode belonging to the seventh of the scale, governs the tonic har mony. Here it belongs to the second or to the fourth of the scale, and receives a different treatment accordingly ; Ex. 11. We shall afterwards find that this combination may be long to the dominant of the major, or to the subdominant of its relative minor ; or, lastly, to the dominant of the sante re lative minor. 1Vre shall, however, find, when we come to :Teak of a system of perfect and untempered harmony, that all the intervals do not exactly coincide in all these cases.