Henrik Ibsen's "The Theater," written in 1851, is here translated into English. Ibsen argues that opera is understood only as a whole: music, libretto, acting, staging, and message.
Harris, John B.
"The Theater (Article by Henrik Ibsen),"
BYU Studies Quarterly: Vol. 4
, Article 7.
Available at: http://scholarsarchive.byu.edu/byusq/vol4/iss1/7