How did chromatic harmony make tonality less clear during the 19th century?

During the 19th century, composers increasingly utilized chromaticism—the use of notes outside the standard diatonic scale—to enhance expressive detail, which gradually destabilized the clarity of tonality.123

Chromatic harmony made tonality less clear through several key methods:

• Ambiguous Chords: Composers employed dissonant, altered chords, such as the augmented sixth chord, which possess an unstable and functionally ambiguous quality. Because these chords can be interpreted in multiple ways (enharmonic equivalence), they blur the listener's ability to perceive a specific key.2
• Delayed Resolutions: By frequently using chains of secondary dominants and chromatic progressions, composers often postponed or evaded the cadences that traditionally defined harmonic direction and established a tonal center.123
• Functional Blur: In works like Richard Wagner’s Tristan und Isolde, the continuous use of chromaticism meant that harmonies often resolved to other unstable chords rather than a tonic. This obscured the sense of functional harmony, making it difficult for listeners to identify a clear home key.23

Ultimately, these techniques shifted the focus from functional, diatonic harmony toward a more complex, coloristic use of dissonance, setting the stage for the eventual dissolution of traditional tonal systems.234