Louis Henry Sullivan was also a philosopher and a writer

One of the most interesting facts about Louis Sullivan is that he began writing after realizing that his career as an architect was about to come to an end. He has penned some philosophical articles and even created his own set of evolutionary hypotheses. Walt Whitman was Sullivan's all-time favorite writer. Also having a big impact on his writing was Spencer's Synthetic Philosophy.

Natural Thinking: A Study in Democracy was a piece that Sullivan wrote in 1905, but it was never published. Sullivan was "the finest philosopher among the American architects, who strove to make architecture a vehicle for democracy," according to the great American historian Henry Steele Commager, who wrote about him.

He was forced to live in a single bedroom in 1920 and was supported by friends because he had no office at all. His desk in the office of a Chicago terra-cotta company eventually became his workspace, where he was able to finish two important tasks: writing his Autobiography and finishing 19 plates for A System of Architectural Ornament According with a Philosophy of Man's Powers (1924).

Understanding Sullivan's architectural idea requires reading both his Autobiography of an Idea (1924) and Kindergarten Chats (published serially in 1901–1922). Eight extra essays by Sullivan are included in the 1947 Wittenborn edition of the later, Kindergarten Chats and Other Writings (rev. 1918), along with a bibliography.