Conceptual art emerged as a movement during the 1960s – in part as a reaction against formalism as then articulated by the influential New York art critic Clement Greenberg. According to Greenberg Modern art followed a process of progressive reduction and refinement toward the goal of defining the essential, formal nature of each medium. Those elements that ran counter to this nature were to be reduced. The task of painting, for example, was to define precisely what kind of object a painting truly is: what makes it a painting and nothing else. As it is of the nature of paintings to be flat objects with canvas surfaces onto which colored pigment is applied, such things as figuration, 3-D perspective illusion and references to external subject matter were all found to be extraneous to the essence of painting, and ought to be removed.