How did basso continuo function in Baroque sonatas?

In Baroque sonatas, the basso continuo functioned as a foundational system of improvised accompaniment that bridged the gap between the treble and bass lines. Because composers typically wrote out only the upper melody parts and a single bass line, the continuo provided the necessary harmonic substance to support the composition.12

The realization of this accompaniment generally involved two types of performers:32
* A chordal instrument: A keyboard player (harpsichordist or organist) or a lutenist who improvised harmonies based on the bass line.12
* A low melody instrument: A performer on an instrument such as a cello, bassoon, or viola da gamba who reinforced the written bass line.12

To guide the improvising musician, composers often used figured bass, a form of musical shorthand where numbers placed above the bass notes indicated the required intervals and chords. This system allowed performers to exercise creative freedom, ranging from simple harmonization to complex, spontaneous counterpoint. As long as the trio sonata remained a central chamber-music medium, the continuo served as a vital sign of the balance between counterpoint and monody, though it eventually declined as composers moved toward more detailed, fully written-out notation.124