Experimental theatre (also known as avant-garde theatre), inspired largely by Wagner's concept of Gesamtkunstwerk, began in Western theatre in the late 19th century with Alfred Jarry and his Ubu plays as a rejection of both the age in particular and, in general, the dominant ways of writing and producing plays. The term has shifted over time as the mainstream theatre world has adopted many forms that were once considered radical. Like other forms of the avant-garde, it was created as a response to a perceived general cultural crisis. Despite different political and formal approaches, all avant-garde theatre opposes bourgeois theatre. It tries to introduce a different use of language and the body to change the mode of perception and to create a new, more active relation with the audience. Relationships to audience Famed experimental theatre director and playwright Peter Brook describes his task as building "… a necessary theatre, one in which there is only a practical difference between actor and audience, not a fundamental one." Traditionally audiences are seen as passive observers. Many practitioners of experimental theatre have wanted to challenge this. For example, Bertolt Brecht wanted to mobilise his audiences by having a character in a play break through the invisible "fourth wall," directly ask the audience questions, not giving them answers, thereby getting them to think for themselves; Augusto Boal wanted his audiences to react directly to the action; and Antonin Artaud wanted to affect them directly on a subconscious level. Peter Brook has identified a triangle of relationships within a performance: the performers' internal relationships, the performers' relationships to each other on stage, and their relationship with the audience. The British experimental theatre group Welfare State International has spoken of a ceremonial circle during performance, the cast providing one half, the audience providing another, and the energy in the middle. Aside from ideological implications of the role of the audience, theatres and performances have addressed or involved the audience in a variety of ways. The proscenium arch has been called into question, with performances venturing into non-theatrical spaces. Audiences have been engaged differently, often as active participants in the action on a highly practical level. When a proscenium arch has been used, its usual use has often been subverted. Audience participation can range from asking for volunteers to go onstage to having actors scream in audience members' faces. By using audience participation, the performer invites the