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.
Copyright arises upon creation and, under current law, endures for the life of the author plus 50 years. (The term of copyright for works created before 1978 is 75 years.) Copyright applies to both unpublished and published works.