Page:Letters to a Young Lady (Czerny).djvu/64

 When to these two voices a third person, with a high male voice, adds his accompaniment, there arises a harmony in three parts.

Lastly, imagine a deep male or bass voice, by way of accompaniment, and we shall have a harmony in four parts, in which each part sings a different melody, and nevertheless the whole together sounds harmonious and pleasing to the ear. You will easily imagine, Miss, that the three singers who accompany the first do not sing at hazard, and merely what may strike them; for this would produce a horrible discordance: consequently the chords of which this four-part harmony consists, are arranged by the composer according to certain rules, in order to produce that fine effect.

Those rules are just what we are taught to know by thorough-bass; and consequently the theory of harmony consists in shewing—

1st. What chords are possible in music; and,

2nd. How these chords must succeed each other in a regular manner, so as to give to each melody the necessary harmonic ground-work, or accompaniment.

“But,” you will ask, “in the pieces which I play, whole lines often occur, in which there are no chords, and nothing but running or skipping passages in one hand, while the other strikes single notes; or there are passages in