A Dictionary of Music and Musicians/Figured Bass
FIGURED BASS is a species of musical shorthand by which the harmony only of a piece is indicated. It consists of the bass notes alone, with figures to represent the chords. It seems to have been first employed by Peri, Caccini, Viadana, and Monteverde, about 1600, in the accompaniments of their Recitatives and Songs, and was afterwards for some time in universal use for accompaniment; songs such as the collection of the Orpheus Britannicus, and anthems such as Boyce's collection, and great works like Bach's Passion and Handel's Messiah, having accompaniments indicated in this manner. The bass line consisted of the lowest part of whatever was going on at the time, whether treble, or tenor, or bass, and in choral works it often leapt about promiscuously in a manner that would be very harassing to a player unaccustomed to the process, as for example
The figures represented the diatonic intervals counting upwards, without reference to the nature of the chord; thus 2 always meant the next diatonic note above—D above C, as in (a), and 4 the next note but two, as (b), and so on up to the 9th, above which the figures of the lower octave were repeated; and the choice of the particular octave in which a note represented by a figure should be placed, as well as the progression of the parts, was generally left to the discretion of the player.
It was not customary to insert all the figures, as some intervals were looked upon as too familiar to require indication, such as the octave and the fifth and the third, or any of them in combination with other intervals; thus a 7 by itself would admit of any or all of them being taken without being indicated, as (c); and a 9 would admit of a fifth and a third, as (d); and a 6 of a third, but not of a fifth, as (e); and a 4 of a fifth and an octave, as (f). When a 2 was written alone over a note it admitted also of a sixth and a fourth, as (g); but more commonly the 4 was written with the 2, and the sixth only was understood; and this seems to be the only case in which notes other than the octave or fifth or third are left to be understood.
When notes were chromatically altered the accidental was added by the side of the figure representing that note (7♭), or for sharpening a note a line was drawn through the figure or by its side, as at (h), and as it was not customary to write the 3, when the third was to be chromatically altered the accidental was placed by itself with the bass note thus a simple ♯, ♭, or ♮, implied a ♯, ♭, or ♮, 3rd. When the bass moved and any or all of the notes of the harmony above it stood still, it was common to indicate this by a line drawn from the figures indicating the notes which remained stationary to the place where they moved again, and if the notes happened to be such as were usually left to be understood by the player, the lines were drawn over the bass from the point in which it began to move under the implied chord. Whenever the bass was to be unaccompanied by harmony, the words 'Tasto Solo' were written.
The figures were usually written in their numerical order, though for special purposes they might be reversed when the composer required a particular disposition of the notes, and similar emergencies often caused the 8 or the 5 or the 3 to be inserted if it was indispensable that the notes represented by those figures should not be missed out.