How did musical Impressionism depart from traditional harmonic relationships?

Musical Impressionism, initiated by Claude Debussy, departed from traditional harmonic relationships by moving away from functional tonality—the system where chords resolve toward a central tonic key. Instead of relying on standard major and minor scales, Impressionist composers utilized several innovative techniques to obscure or abandon traditional harmonic motion:

• Whole-Tone Scales: Debussy employed scales composed entirely of whole steps. Because these scales lack the specific distribution of whole and half steps found in traditional scales, they prevent the formation of perfect fourths and fifths, effectively removing the foundation of traditional harmonic resolution.12
• Self-Sufficient Dissonance: Impressionism treated dissonant chords, such as seventh chords, as self-sufficient entities rather than as tensions requiring resolution to a consonance. This allowed for parallel movement of chords, which blurred the sense of traditional harmonic progression.1
• Static Harmony: By prioritizing instrumental timbre and "colour" over directed melodic or harmonic motion, composers created static harmonic environments. This approach disrupted the forward-moving rhetoric of Romanticism, favoring a shimmering, atmospheric effect over the goal-oriented cadences of the common practice period.31