Debussy wanted to distance himself from what he considered the emotional excess of the Romantics and instead wanted to write music that, through sound, created an ambience similar to that of the Impressionist painters and Symbolist poets of his day.
All books initially copyrighted in the US from 1964 through 1977 have had their copyrights automatically renewed (by law) and the copyrights are still in force. The initial copyright term was 28 years; the renewal was for 67 more years.
Every book and artwork created before the introduction of copyright is in the public domain. In the United States copyright begins with the Constitution in 1787. Every work created before 1787 is under public domain, and every work that was copyrighted and has had its copyright expired is also under public domain.