121. Of discords by addition, the most important are the dominant seventh and its derivatives. This chord is pro duced by adding to the harmony of the dominant, or com mon major chord of the fifth of the key, its minor seventh, which is the fourth of the scale; Nos. 1. and 2. In this combination, the most remarkable thing, and what most at tracts the attention of the ear, is the lesser fifth between the third and seventh of the cltord, that is, between the major seventh and perfect fourth of the scale. The resolution of this discord is by the moveme_nt of its two parts towards each other, each by one degree of the diatonic scale, so that they meet in a third major or minor according to the mode, Nos. 3. and 4. Or if the position of the eltord invert this lesser fifth into a greater tburth, the resolution is by the movement of tlte two parts which form this interval from each other to a sixth minor or major according to the mode, Nos. 5. and 6.; and N% hen the bass of the dominant, at the same time, falls a fifth, or rises a fourth to the key note, the whole progression is of the most satisfactory and conclusive nature. This is called the perfect cadence; but, as we ob served, Art. 103. accent and rhythm contribute essentially to this conclusive effect, which we shall take an opportunity afterwards of illustrating with the fulness that its importance demands. Kirnberger and his followers call this the essen tial discord; but though we allow that the addition of the seventh to the dominant chord greatly heightens its effects, and makes it indicate still more expressly the succeeding to nic harmony, we cannot allow that the seventh is essential to the progression, or to its conclusive nature, and therefore we shall not adopt this phraseology. That our readers how ever may not misunderstand us, and suppose that we mean to say that this discord might be spared, we shall quote a sentence from Mr. Shield to show its importance. " The modern elegant Italian masters have produced, and do daily produce many charming compositions, without the assistance of any other discord than this minor seventh and its deriva tives, when judiciously blended with concords." 7 This chord is figured a, or simply with 7. But in the minor mode the major third to the bass is intimated by, a * placed below the other figure or figures as in Nos. 2, 4, 6. When by means of this chord the modulation is carried into another key, which requires an accidental sharp to make the leading chord major, this accidental is indicated by a* un der a 7, as in No. 7'; and when the modulation goes to a key which requires an accidental flat to make the seventh minor, this is signified by the flat character before the figure, as in .No. 8.
As, by the resolution, the third and seventh have a deter mined movement, they ought not to be doubled. In com positions of many parts the third may be doubled, being re solved only in that part where it is most conspicuous. We shall even sometimes find the seventh doubled and resolved only in one part.* The bass and fifth may be doubled in the octave or unison. In omitting parts of the chord, the octave to the bass, and the fifth, ought to be left out rather than the third, because this last characterizes the chord as the dominant. Cases however will occur when the third inay fall to be omitted. If the seventh be left out, the chord is the common major chord of the fifth of the key; but as we have before said, it is still the dominant or leading chord in final cadences.
The dominant chord 'of seventh may be considered, as we have observed, Art. 116. as formed by the union of the
major chord of the filth of the key, and of the imperfect common chord of the major seventh of the scale. This last chord of itself most naturally points to the common chord of the key, No. 9; and all its inversions lead to the same harmony. See examples, Art. 116. Nos. 5, 6, 7, &c.
As the two chords, therefore, point to the same succeeding harmony, and as their union Ibrms a chord far front disa greeable, though requiring resolution, nothing can be more pleasing and satisfactory than this progression.
The chord of dominant seventh has different positions; and by the resolution the succeeding tonic harmony is placed in different positions. We shall therefore exhibit the chief of these with the resolutions, in four parts.
When the seventh is highest, the succeeding chord, by the resolution, has the third uppermost, No. 10, a, 1), c, d. At a, the fifth of the leading chord may either rise, which doubles the third of the tonic, or it may fall on the octave, which is better ; or in compositions for several voices or in struments, the fifth of the leading chord may fall on the fifth of the tonic, crossing the part in which tlte sensible note rises to the resolution on the octave; but then the bass and fifth must go in contrary motion, as at I ; and this 'flannel. of taking the harmony may be allowed on keyed instruments. At c, the octave to the bass is taken, and the fifth omitted; and in this form the progression phrases better then the others, as each part is kept in its own place, and the har mony of the tonic is full. At d, the fifth is placed an octave lower than in the preceding examples. It may fall on the octave, or go to the fifth by contrary motion to the bass. Mr. Kollmann, indeed, positively allows WO in simi lar motion in the progression of the dominant to the key, and vice versa.
If the fifth of the leading chord be ltighest, it naturally re solves on the octave position of the tonic, No. 11, a, b, c, d. At a, the leading note and fifth meet in unison on the key; or these parts may cross as at b, which, however, is not very good here, as the highest part ought to keep its place. At c, the sensible note is placed an octave lower, which makes the harmony more dispersed. At d, the octave to the bass is taken, and the sensible note omitted, which makes the conclusion less marked, and therefore less proper for the final close of a strain.
When the third of the dominant is highest, it necessarily resolves on the octave position of the tonic, No. 12, a,b, c., d. The two last, in which the octave is taken instead of the fifth of the leading cltord, phrase better than the others, and give the tonic harmony full.
\Then the octave to the bass is highest, it naturally' makes the tonic harmony in the position of fifth, which is the least conclushe, and therefore seldom found as a final close, 13, (1, b. The extreme parts in full harmony may, however, meet on the octave by contrary motion, as at c.
The dominant chord, without the seventh, leads very well to the first derivative of the chord of the key, as No. 14, a; but when the seventh is added, this progression cannot very well take place, because the resolution of the seventh on the octave to the note taken by the bass, has an effect similar to consecutive octaves, b. This progression, however, is some times practised in full harmony, which is a license; but in that case the resolution being taken by the bass, the seventh descends a fourth to double the sixth as at c, or ascends to the third as at d.