Participatory art is an approach to making art which engages public participation in the creative process, letting them become co-authors, editors, and observers of the work. This type of art is incomplete without viewers' physical interaction. It intends to challenge the dominant form of making art in the West, in which a small class of professional artists make the art while the public takes on the role of passive observer or consumer, i.e., buying the work of the professionals in the marketplace. Commended works by advocates who popularized participatory art include Augusto Boal in his Theater of the oppressed, as well as Allan Kaprow in happenings.