The opera demands the poet and the composer; and yet the text of the opera is a work of literature independent and complete in itself, and the music of the opera has its own life.

Again, every musical work demands the performer.

The orchestra must play the symphonies, the pianist or the singer must make the melodies living, the actors must play the drama.

But the music is a perfect work of art even before it is sung or played on an instrument, just as a drama is complete as a work of literature even if it never reaches the stage.

Moreover it is evident that the realization by actors is needed for the photoplay too.