If defined in regards to time scale, Modernism is seen as the time before World War 2 and Post-Modernism after. If defined according to ideology, most definitions suggest that Postmodernism rejects the concept of advancement or progress in art.
Post-modernists believe that their work, their processes and their ideological values are contemporary, but in truth, they have their origins in the early 20th century. Specifically, their ideological values can be traced back to the work of Marcel Duchamp from 1913 to 1923.
After the Second World War, such optimism in the future was difficult to sustain. And to make things worse, with the advent of the Cold War and the constant threat of nuclear destruction, any sort of future looked doubtful.
Having rejected the past many years ago, and now with the future no longer the goal of artistic effort, many artists turned with visible concern to the present and focused their attention on contemporary popular culture.
Popular culture, however, was undergoing a wild disruption during the sixties: the Civil Rights movement, opposition to the Vietnam war, the emergence of a widespread women's movement.
Pop artist could still appear progressive under these circumstances, contributing a critique of middle class ideals and the American dream (for example, Richard Hamilton).
Just What Is It That Makes Today's Home So Different, So Appealing?
1956, Collage (Kunsthalle Museum, Tübingen, Germany)