Figured Bass
From DIMA
Author : Erich Türk
A vast area of the chamber repertory of the organist is provided by the pieces written in figures bass, this being basically the pillar of chamber music, orchestral and coral literature of the Baroque. The organ is only one in the multitude of harmonic instruments which can be used to write the figured bass, the sources of the age point out also the lute, harp, theorbo, harpsichord etc.
If in the early years of the 17th century there are only seldom mentioned differences between the organ playing style and the harpsichord one, with Agostino Agazzari we find in 1607 a first seed of this idea. Towards the end of the 17th century this difference begins to be deeper.
Of the procedures typical for the harpsichord Lorenzo Penna notes: doubled voices, trills, acciaccaturas, reiteration of chords and the arpeggio. A fist reason to arpeggiate is the one of clarity: the short duration o f the sound of the harpsichord does not always allow the intervals to be understood, and therefore a short arpeggio will render more intelligible the progression of the voices. There are also expressive reasons for the arpeggios: very different effects may be obtained, its character being lyric or dramatic, rhythmic or free, pathetic or sober. The indications of Francesco Geminiani also reveal the necessity of an almost permanent movement in the harpsichord accompaniment.
These procedures were not applied exclusively to the harpsichord, as proved by the following quote from the treatise by Andreas Werckmeister: the soloists and instrumentalists must play the passages and coloraturas on the background of the chord in the figured bass --- the organist should not behave all the time as if playing at a peasants' wedding.
Johann Sebastian Bach: Ich ruf zu dir, Herr Jesu Christ BWV 639
Also, the procedure of reiterated chords is found for instance with Georg Böhm, in the Vater unser im Himmelreich chorale. Here, the ornamented choral in the soprano is practically accompanied by a basso continuo in harpsichord style (repeated chords, trills, mordents, passage notes etc.):
Georg Böhm, Vater unser im Himmelreich
In conclusion, although the style of playing the figured bass on the organ is certainly more restrained than on the harpsichord, an organist can use the entire arsenal of the means of ornamentation, to apply them in the spirit of the music he plays and within the boundaries of common sense, the latter being the essential condition of a good musician, unanimously recognized in the theoretical treatises.