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.
And, if the work is a work for hire, or anonymous or pseudonymous, the term of protection is the shorter of 95 years from first publication, or 120 years from the date of creation. Consequently, no post-1978 works are scheduled to fall into the public domain until the middle of the 21st Century. According to a 1961 Copyright Office study less than 15% of all registered copyrights have been renewed. For books and other textual materials, that number jumps to more than 90%.