Harmony in Impressionism

Composers began to use harmony like colour. Different chords could coexist and did not need to be resolved as usual. Chords either create tension or resolve it, and generally we expect a tension-creating harmony to be resolved, but Impressionism consciously worked against these expectations. The harmonies here include dissonances or vertically broad chords of stacked thirds (with ninths and elevenths), whole-tone scales and pentatonic scales, and harmonies made up of fourths and fifths.