How does rhythm determine when harmonies change in a piece of music?

In music, rhythm and harmony are inextricably linked, as rhythm organizes harmony in time and determines when chords change. This specific time pattern controlling the pace of harmonic change is known as harmonic rhythm.123

The relationship functions in the following ways:

• Defining Flow and Structure: Harmonic rhythm dictates the energy and drive of a piece. A frequent change of chords relative to the musical rhythm creates a rapid harmonic rhythm, while a leisurely pace of change results in a slow harmonic rhythm.43
• Creating Contrast: By varying the harmonic rhythm within a composition, a composer can create contrast, which helps define sections of musical form.3
• Regulation of Dissonance: Historically, rhythmic placement was used to manage dissonance. In early harmonic writing, dissonant intervals were often confined to the "weak beats" of the musical meter and resolved through stepwise movement to consonant intervals.3
• Integration with Meter: In many Western musical traditions, the rhythmic structure is inseparable from harmonic considerations, as the underlying meter often provides the framework upon which harmonic changes are articulated.25

Ultimately, harmonic rhythm serves as a fundamental tool for composers to establish points of articulation, build tension, and provide resolution throughout a piece.43