How can notes played one after another create an impression of harmony?

Although harmony is traditionally defined as the simultaneous sounding of two or more notes, the human ear can perceive an impression of harmony even when notes are played one after another. This occurs because the brain processes these successive notes by referencing familiar chords—groups of notes that would typically sound together—and mentally synthesizing them into a simultaneous harmonic structure.1

This phenomenon is similar to how the eye perceives motion in a motion picture through a rapid succession of still images. Composers often utilize this effect through techniques such as:1

• Arpeggiated chords: Playing the notes of a chord in a melodic, sequential fashion rather than simultaneously.2
• Scale passages: Using melodic lines that clearly outline the tonality and harmonic direction of a composition.2

By employing these styles, a single melodic line can imply a complex underlying harmonic framework, allowing the listener to perceive the "vertical" logic of harmony within a "horizontal" melodic progression.21