Explain why some critics explain conceptual art as an attack on the economics of art.

Conceptual art is the artistic movement that began between 1966 and 1972. 
Amongst its most famous artists at its early stage were artists such as Joseph Kosuth, Robert Morris, Joseph Beuys, Adrian Piper. 
Conceptual artist produce works and writings that completely rejected standard ideas of art. According to them all art is essentially conceptual. Conceptual artists reduce the material presence of the work to an absolute minimum - a tendency why some critics explain conceptual art as and attack of the economic of art  and as the "dematerialization" of art. 

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