I would like to analyze Brecht's theory of theater in light of the science of theater arts (Theaterwissenschaft). New findings confirm Brecht's most important contribution to theater has been ”Zuschaukunst” (the art of spectators). This is not only a theory on the origin of art, but also includes the basis of his theory and practice. Role observations, demonstration and critiques of actors replace the traditional Aristotelian theory of theater. In this way, the audience can identify with the actor's roles and fall into a state of illusion. This revolutionary theatrical experience is thus termed ”Zuschaukunst”. An intra-theatrical transaction emerges when an audience starts to observe and criticize. This attitude helps the audience reform society and preserve national security.