What musical features in Gustav Mahler’s works anticipated 20th-century composition techniques?

Gustav Mahler is recognized as a pivotal figure whose work bridged the late Romantic era and the innovations of the 20th century. His compositions anticipated several radical methods that would define modern music.12

Key features in Mahler’s works that foreshadowed 20th-century techniques include:

• Progressive Tonality: The practice of ending a composition in a different key than the one in which it began, challenging traditional expectations of tonal unity.13
• Dissolution of Tonality: Through constant use of chromaticism and harmonies outside of the established key, Mahler obscured the listener's perception of a central tonal center.1
• Contrapuntal Texture: A shift away from block-chordal harmony produced by the full orchestra toward a texture based on interwoven melodies for solo instrument groups.1
• Thematic Variation: A focus on the continuous development and variation of themes rather than simple restatement.1
• Ironic Quotation: The deliberate inclusion of popular styles and everyday sounds, such as bugle signals or bird calls, to create contrast and cynicism.14
• Cyclic Structure: The use of themes or motives shared across different movements to unify the symphony.14