Master the vertical dimension of music—how multiple pitches sound simultaneously to create chords, progressions, and emotional color. Harmony provides context and emotion for melodies. Learn: chord construction (triads: root-third-fifth), qualities (major=happy, minor=sad, diminished=tense, augmented=mysterious), inversions (different bass notes), and extensions (7ths, 9ths add sophistication).
Study progressions: I-IV-V (three-chord songs), ii-V-I (jazz standard), I-V-vi-IV (pop everywhere). Understand: consonance (stable, pleasant) vs dissonance (tension, wants resolution). Train ears to hear chord changes. Practice: singing harmony parts (thirds, fifths above melody), analyzing songs' progressions, playing chord progressions. Functional harmony (classical) vs modal harmony (folk/rock).
Harmony transforms single-note melodies into rich, emotional landscapes. Essential for composers, arrangers, accompanists.