A shift of such magnitude does not come overnight, nor as the feat of one artist alone. Portents and antecedents become increasingly recognizable in retrospect — Monet’s Nymphéas or Mondrian’s transmutation of sea and sky into signs plus and minus. And the picture planes of a Synthetic Cubist still life or a Schwitters collage suggest like-minded reorientations. But these last were small objects; the ‘thingness’ of them was appropriate to their size. Whereas the event of the 1950s was the expansion of the work-surface picture plane to the man-sized environmental scale of Abstract Expressionism. Perhaps Duchamp was the most vital source. His Large Glass begun in 1915, or his Tu m’ of 1918, is no longer the analogue of a world perceived from an upright position, but a matrix of information conveniently placed in a vertical situation. And one detects a sense of the significance of a ninety-degree shift in relation to a man’s posture (even in some of those Duchamp ‘works’ that once seemed no more than provocative gestures: the Coatrack nailed to the floor and the famous Urinal tilted up like a monument.
–Leo Steinberg (1968)
One of the first applications of the term postmodernism to the visual arts occurs in Leo Steinberg’s “Other Criteria” in the course of a discussion of Robert Rauschenberg’s transformation of the picture surface into what Steinberg calls a ‘flatbed,’ referring, significantly, to a printing press. This flatbed picture is an altogether new kind of picture surface, one that effects, according to Steinberg, “the most radical shift in the subject matter of art, the shift from nature to culture.” That is to say, the flatbed is a surface which can receive a vast and heterogeneous array of cultural images and artifacts that had not been compatible with the pictorial field of either premodernist or modernist painting.
–Douglas Crimp (1980)
UNSAID: noun /uhn•'sed/ 
