Reading and Realizing Figured Bass

Baroque keyboard players did not read out fully written chords. They read a bass line with small numbers under certain notes, called figures, and built the harmony themselves on the spot. This worked because the figures do not name pitches directly. They count intervals above whatever bass note is written, so the same figure produces different actual notes depending on the bass. A keyboard player who knew the key and the rules of voice leading could turn that shorthand into a full texture of chords, filling in alto, tenor, and soprano parts above the given bass.

The default figure for a root position triad is 5 3, often left unwritten since it is assumed unless other numbers appear. A 6 means first inversion: add a third and a sixth above the bass, since the bass itself is the third of the chord. A 6 4 means second inversion: add a fourth and a sixth above the bass, since the bass is the fifth of the chord. Sharps, flats, or naturals next to a figure tell you to alter that interval above the bass, not to alter the bass note itself. Reading figured bass is really just interval counting: take the bass pitch, count the stated number of scale steps upward, and check the key signature or accidental to get the exact note.

This connects directly to inversions read from Roman numerals. A 6 chord is the figured bass twin of a first inversion triad, and 6 4 matches second inversion. Once seventh chords enter the picture, figures like 7, 6 5, 4 3, and 4 2 extend the same logic to four-note chords stacked in thirds.