How did Louis Sullivan’s ornament differ from Gothic Revival and Queen Anne decoration?

Louis Sullivan’s approach to ornament represented a departure from the historical eclecticism that characterized the Gothic Revival and Queen Anne styles. While his early work maintained some links to these movements, his mature style was fundamentally different in its origin and intent.1

• Rejection of Historical Precedent: Unlike the Gothic Revival, which relied on the scholarly or picturesque reproduction of medieval forms and details, Sullivan’s ornament was not based on historical imitation. He viewed the adoption of past styles as a false principle, believing instead that architecture should express the environment and the specific nature of the building.123
• Natural and Geometric Basis: Sullivan’s mature ornament was derived from geometry and the stylized forms of nature rather than the revival of specific architectural periods.1
• Integration with Form: Sullivan sought to permeate his structures with a single, cohesive spirit, ensuring that ornament was not merely applied decoration but an integral part of the building's mass and detail.1

Ultimately, Sullivan’s work moved away from the "frigidly correct" archaeological reproductions often found in late 19th-century revivalist architecture, favoring a unique, fluid, and exuberant expression that he felt could "illuminate the heart".14