Why did Louis Sullivan oppose copying historical architectural styles?

Louis Sullivan opposed copying historical architectural styles because he believed that adopting a style created by a different age was a "false principle". He argued that true architecture must be born from the intellectual and moral forces of its own society, serving as an authentic expression of that specific civilization.1

Sullivan’s philosophy was rooted in the belief that architecture should evolve from and express its environment, function, and structural basis rather than relying on historical precedent. He viewed the imitation of past forms as a failure to address the unique requirements of modern construction, such as the skyscraper. For Sullivan, architecture was a creative endeavor that should illuminate the heart and reflect the spirit of its own time. Consequently, he rejected the "historical eclecticism" prevalent in his era, famously protesting the use of classical adaptations at the 1893 Columbian Exposition, which he believed hindered the development of a progressive, indigenous American architecture.12