IVe tnust avoid, a fifth, after a unison, by similar motion. It is good in oblique motion, and is allowed in contrary mo tion, one part moving a single degree ; Ex. 3d. Front the unison we may go to the sixth minor, by contrary motion. It is not very good by the other motions, because of the large leap ; Ex. 4th. But it is forbid to go from the unison, to the sixth major. We must avoid an octave after the unison, ex cept by oblique motion: for this, as in two unisons, is but as the division of a large note into smaller." From the fifth to either sixth, is best by oblique motion; it is also allowed by similar motion, one part moving a sin gle degree; and it is allowed ascending, but not descending, to go by a leap from the fifth to the sixtlt minor, but not to the major. In passing front the fifth, through the sixth, to the octave, the sixth must be major, never minor, and that by contrary, 'notion.
These rules for the unison, 1NIr. Shield gives from Dr. Pe pusch, " whose treatise," he observes, " is dated in 1731; consequently contains many exploded doctrines; but it like wise contains principles which will be the basis of theory in 1800, or any other century." The following law respecting fifths, Mr. Shield says, was laid down by an excellent judge, and has been so much re spected, as to be generally obeyed by correct writers, for more than half a century. " From the fifth to the unison is g,00d, by oblique motion; we may also go by contrary mo tion, one part moving a single degree; but it is bacl by si milar motion.
From a fifth we may go to either third, by all the motions, but best by the oblique. The next best way to the third :ninor, is by contrary motion, and to the third major is by the similar; both these by single degrees.
A false fifth or seaddiapente, may immediately follow a perfect fifth, provided it be also immediately succeeded by a third gradually, and by contrary motion.
We must avoid an octave after a fifth by. leap, in similar motion. It is good by oblique and contrary motion, and may be allowed in similar motion, one part moving a single degree." This last example, we may add, in which the octave fol lows the fifth descending, the upper part fallit:g a tone, is quite classical, and universally practised.
101. We now proceed to consider the combinations of in tervals in chords, and the manner in which chords may suc ceed each other. When a note is sounded along with its third and fifth, midi or without the octave, the combination is called a common chord. The Germans call it a triad, which name is adopted also by Dr. Callcott, in his Alusical
Grammar. Common chords are distinguished into major and minor, according as the third is major or minor. The difference in the effects of these two kinds of chords is very striking. The distinction is one of the most iinportant in ancl is what chiefly constitutes the major and minor modes, as already observed.
102. From the tables of the major and minor intervals in the diatonic scale, given in alt. 78, it is easy to see what common chords are major, and what arc minor. In the ma jor mode, the common chord to the lowest note of the scale, which is called the key-note, the chord of the fifth of the scale, and that of the fourth of the scale, are major. The chords of the second of the scale, of the third, and of the sixth of the scale, are minor. The chord formed by the seventh of the scale, with its third and fifth, differ; from all these, as the fifth is imperfect, which is a discord. This is therefore called the impel feet, or dissonant cotnmon chord. These we exhibit in the major mode of C, leaving it to the industry of the student, to write them in other ken or scales.
All these chords are occasionally used in a piece of har mony in the major mode, but they are by no means all of equal importance, or of equally frequent use.
103. The most important of all these chords is that of the key ; it is called the harmony of the key, or the tonic harmony; with this harmony, every regular piece of music in the major inode begins and ends. All the other chords must proceed regularly from this, and return to it in such a manner as to heighten its effects.
104. The next chord in point of importance and fre quency-, is that of the fifth of the scale. These two chords succeed each other in a very agreeable and natural manner, whether we go from the chord of the key to that of its fifth, or in the inverse order; Ex. 1.
The last of these two progressions, namely, from the har mony of the fifth of the key to that of the key itself, is al most always the concluding progression in any piece of mu sic. It is called the peifect cadence, or close, and is the most conclusive and satisfactory progression in harmony; but how much accent and rhythin contribute to this conclu sive effect, will be seen afterwards.
From this effect, the harmony of the fifth of the key is called the leading chord ; and it is also called the dominant chord, because it governs or requires the tonic harmony to succeed it.