Figured bass

Basso continuo parts, most common in the Baroque era (1600–1750), provided the harmonic structure of the music by supplying a bassline and a chord progression.

At least one instrument capable of playing chords must be included, such as a piano, harpsichord, organ, lute, theorbo, guitar, regal, or harp.

Sometimes instruments are specified by the composer: in L'Orfeo (1607) Monteverdi calls for an exceptionally varied instrumentation, with multiple harpsichords and lutes with a bass violin in the pastoral scenes followed by lamenting to the accompaniment of organo di legno and chitarrone, while Charon stands watch to the sound of a regal.

The keyboard (or other chord-playing instrument) player realizes (adds in an improvised fashion) a continuo part by playing, in addition to the notated bass line, notes above it to complete chords, either determined ahead of time or improvised in performance.

Experienced players sometimes incorporate motives found in the other instrumental parts into their improvised chordal accompaniment.

Modern editions of such music usually supply a realized keyboard part, fully written out in staff notation for a player, in place of improvisation.

[3] A late example is C. P. E. Bach's Concerto in D minor for flute, strings and basso continuo (1747).

The phrase tasto solo indicates that only the bass line (without any upper chords) is to be played for a short period, usually until the next figure is encountered.

For example, if a continuo part in the key of C begins with a C bass note in the first measure, which descends to a B♮ in the second measure, even if there were no figures, the chord-playing instrumentalist would deduce that this was most likely a first inversion dominant chord (spelled B–D–G, from bottom note of the chord to the top).

In the 20th and 21st century, figured bass is also sometimes used by classical musicians as a shorthand way of indicating chords when a composer is sketching out ideas for a new piece or when a music student is analyzing the harmony of a notated piece of music (e.g., a Bach chorale or a Chopin piano prelude).

In the 2000s, outside of professional Baroque ensembles that specialize in the performance practice of the Baroque era, the most common use of figured bass notation is to indicate the inversion in a harmonic analysis or composer's sketch context, however, often without the staff notation, using letter note names followed with the figure.