This discussion is one of the most important in the entire [study of] composition. Whoever knows how to combine three voices well, will likewise find it easy to construct a harmony of many voices. The main harmonic framework depends upon three-part composition. Indeed, the entire effect of the harmony proceeds chiefly from that basis. It can conveniently be divided into two classes, natural and artificial construction. In the former class all three voices are merely drawn from the three chords, and the upper voice constantly asserts its authority as the primary voice, while the second voice neither ascends above it nor introduces anything concerting or imitative, but simply proceeds with the bass according to the rules of harmony. In this way, the melody of the upper voice is never interrupted. One sees many pieces of this type, even by renowned masters, in which neither the second voice nor the bass have any imitation. The second class, on the contrary, is a product of the aforementioned artificial construction. Here nature and art must be united to produce true beauty. The second type is characterized by the three motions of the voices, the imitation of a melodic motif in all three voices, concerting in some passages, the alternation of the brilliant and singing styles, beautiful symmetry or division of the main melody, along with the varying of the harmony by means of forte and piano.