The Eighteenth Century
The need to guide performers in the harmonic and stylistic choices resulted in the regole d'accompagnamento, which begin to appear at the beginning of the eighteenth century. There are a specific set of rules that explain where, rhythmically, chords should be placed according to the movement of the bass, and instructions on how unfigured basses should be harmonized. Eighteenth-century Italian compositional style is concentrated principally in the writing for voice or violin or, in orchestral pieces, in the writing for strings; it has been noted that the harmonic structure is often simple and any counterpoint in the upper voices of the score was expected to be reduced to harmonic blocks in the continuo realization. The instructions on playing harmonically were also in contrast to the required manner of accompanying on the organ in church music, for a clear distinction is always made between styles of accompaniment on the two keyboard instruments.