An Illegal Chord?

In 1899, the man who would one day become John Cage’s teacher wrote a string sextet called Verklärte Nacht (Transfigured Night). It was one of Arnold Schoenberg’s first major works, and it went on to become his most popular; but to the Viennese jury that considered it for performance, Verklärte Nacht proved unacceptable.
Schoenberg, the jury members pointed out, had written a chord that didn’t exist; it was not to be found in any textbook; it was, if you like, illegal.

From Andrew Ford, one of Van Morrison’s biographers.

How often do we treat new ideas like this? Or new approaches? New ways of doing things?