In the arts and in literature, the term avant-garde (advance guard and vanguard) identifies a genre of art, an experimental work of art, and the experimental artist who created the work of art, which usually is aesthetically innovative, whilst initially being ideologically unacceptable to the artistic establishment of the time. The military metaphor of an advance guard identifies the artists and writers whose innovations in style, form, and subject-matter challenge the artistic and aesthetic validity of the established forms of art and the literary traditions of their time; thus how the artists who created the anti-novel and Surrealism were ahead of their times. As a stratum of the intelligentsia of a society, avant-garde artists promote progressive and radical politics and advocate for societal reform with and through works of art. In the essay "The Artist, the Scientist, and the Industrialist" (1825) Benjamin Olinde Rodrigues’s political usage of vanguard identified the moral obligation of artists to "serve as [the] avant-garde" of the people, because "the power of the arts is, indeed, the most immediate and fastest way" to realise social, political, and economic reforms. In the realm of culture, the artistic experiments of the avant-garde push the aesthetic boundaries of societal norms, such as the disruptions of modernism in poetry, fiction, and drama, painting, music, and architecture, the occurred in the late 19th and in the early 20th centuries. In art history the socio-cultural functions of avant-garde art trace from Dada (1915–1920s) through the Situationist International (1957–1972) to the Postmodernism of the American Language poets (1960s–1970s). History The French military term avant-garde (advanced guard) identified a reconnaissance unit who scouted the terrain ahead of the main force of the army. In 19th-century French politics, the term avant-garde (vanguard) identified Left-wing political reformists who agitated for radical political change in French society. In the mid-19th century, as a cultural term, avant-garde identified a genre of art that advocated art-as-politics, art as an aesthetic and political means for realising social change in a society. Since the 20th century, the art term avant-garde identifies a stratum of the Intelligentsia that comprises novelists and writers, artists and architects et al. whose creative perspectives, ideas, and experimental artworks challenge the cultural values of contemporary bourgeois society. In the U.S. of the 1960s, the post–WWII changes to American culture and society allowed avant-garde artists to produce works of art that addressed the matters of the day, usually