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A method of notating the harmonic and rhythmic structure of a piece of music, without explicitly writing every note. Figured bass is notated by writing out a bass line and figures that indicate what kind of chord to build on top of it. Playing from this notation is called realizing a figured bass, and is essentially improvisation because the chords that are indicated can be built in more than one way.

Figured bass was used mainly during the Baroque era (especially by Bach) for notating continuo, the light ensemble used for accompaniment; this usually consisted of a keyboard instrument such as harpsichord or organ and a low string instrument, usually cello or string bass. However figured bass is also used today in music theory education, because it provides a convenient notation for studies of harmony, part writing and voice leading.

As was mentioned before, figured bass is written as a bass line, which provides the lowest note of the chord and the rhythmic structure. Below each bass note, there can appear a figure that indicates exactly what kind of chord should be built on that note. Absence of a figure implies that the chord is a simple chord of the root, third, and fifth in root position (meaning the root is in the bass). So a C in the bass with no figures underneath would indicate that the chord is a C chord, and thus can be constructed of C, E, and G in no particular order. Note that in realizing a figured bass, you never introduce accidentals unless they're specifically indicated.

The following figures are used to indicate the structure of the chord (stacked vertically in real figured bass, but no way to do that here). In bold is what is written, followed what it designates in full, followed by a brief summary:

  • 6: 6 3, first inversion
  • 6 4: 6 4, second inversion
  • 7: 7 5 3, seventh chord in root position
  • 6 5: 6 5 3, seventh chord in first inversion
  • 4 3: 6 4 3, seventh chord in second inversion
  • 2: 6 4 2, seventh chord in third inversion
  • 9: 9 7 5 3, ninth chord in first root position

Other combinations of numbers may be written to indicate voice leading. A number of chromatic alterations can be indicated as well: a sharp next to or a line through a number indicates that degree is to be raised by one half-step, and if a sharp is not next to a number, is assumed to mean the third. Likewise with flats, double sharps or double flats.