Which instrument is considered the core of jazz rhythm sections?

The bass is considered the core of jazz rhythm sections because it provides the harmonic foundation and establishes the underlying structure of the music. In jazz, the bass typically plays a walking bass line, which connects chords and creates a sense of movement and swing that is essential to the style. This rhythmic and harmonic function supports both the soloists and the ensemble, making it a vital instrument in maintaining the groove and pulse of jazz compositions.

While the piano and drums also play significant roles in jazz rhythm sections—creating chords and maintaining tempo respectively—the bass uniquely anchors the harmonic progressions and supports the rhythmic feel of the music. The trombone, while a valuable melodic instrument, does not fulfill the foundational rhythmic and harmonic role that the bass does in this context. Thus, the bass emerges as the central figure in maintaining the cohesion and drive of jazz rhythm sections.