Greenberg made his name as an art critic with his essay Avant Garde and Kitsch, published in 1939. In this article Greenberg claimed that avant-garde and Modernist art was a means to resist the 'dumbing down' of culture caused by consumerism. Greenberg termed this 'kitsch', a word that his essay popularised, though its connotations have since changed. Modern art, like philosophy, explored the conditions under which we experience and understand the world. It does not simply provide information about it - in the manner of an illustratively accurate depiction of the world.
For Greenberg Modernism provided a critical commentary on experience. It was constantly changing to adapt to kitsch culture, which was itself always developing. In the years after World War Two, Greenberg came to believe that the best avant-garde artists were emerging in America rather than Europe. He promoted the work of Pollock and the other Abstract Expressionists as next stage in Modernist art, arguing that Modernist art was moving towards greater emphasis on the 'flatness' of the picture plane.
These views led Greenberg to reject Pop Art in the 1960s, which was influenced by kitsch culture.