Among those atonal works was his second, "Concord" piano sonata, one of the finest, and some would say the finest, works of classical music by an American. It reflects the musical innovations of its creator, featuring revolutionary atmospheric effects, unprecedented atonal musical syntax, and surprising technical approaches to playing the piano, such as pressing down on over 10 notes simultaneously using a flat piece of wood.
What a mischievious creative genius!
And yet, despite the musically innovative nature of these works, from a thematic standpoint, they are strictly 19th century. Ives, like American band-composer Sousa, consciously infused patriotic or "blue-blood" themes into his pieces. In the "Concord," he attempted to project, within the music, the 19th century philosophical ideas of the American Transcendentalists, who obviously had a great impact on his world-view.
Thus, while other atonal composers such as Schoenberg or Berg attempted to infuse their music with "20th century" themes of hostility, violence and estrangement within their atonal music, the atonal music of Ives is, from a thematic standpoint, really quite "tonal."
Ives wrote the following essays as a (very big) set of program notes to accompany his second piano sonata. Here, he puts forth his elaborate theory of music and what it represents, and discusses Transcendental philosophy and its relation to music. The essays explain Ives' own philosophy of and understanding of music and art. They also serve as an analysis of music itself as an artform, and provide a critical explanation of the "Concord" and the role that the philosophies of Emerson, Hawthorne, Thoreau and the Alcotts play in forming its thematic structure.