from The Treachery of Images, Rene Margitte, 1928.
Surrealism started as a response to the rigorous training and analysis of Academic arts. It espoused that Reason and Logic were meaningless. It is also espoused a means of viewing objects and images as free from function customarily ascribed to them. Hence, the above image, that very simply states that this pipe is not a pipe.
Surrealist thought influenced far into the 20th century with adherents such as Dali, Magitte, Duchamp, and into philosophers such as Foucault, Sartre, Gramsci, writers (most specifically in Russia and the American South) such as Faulkner, Kharms, Zoshenko, &c. Above all else, its themes run countercultural to Western organized thought in which existence is rigidly ordered. Often Surrealism served as the only means to criticize political and cultural institutions and in the case of Warhol (though he was more postmodern, pop art) to insult the American Capitalist Iconography.