Though never a self-proclaimed movement, Minimalism refers to painting or sculpture made with an extreme economy of means and reduced to the essentials of geometric abstraction. It applies to sculptural works by such artists as Carl Andre, Dan Flavin, Donald Judd, Ellsworth Kelly, John McCracken, Robert Morris, Richard Serra, Tony Smith, and Anne Truitt; to the shaped and striped canvases of Frank Stella; and to paintings by Jo Baer, Ellsworth Kelly, Robert Mangold, Brice Marden, Agnes Martin, and Robert Ryman. Minimalist art is generally characterized by precise, hard-edged, unitary geometric forms; rigid planes of color—usually cool hues or commercially mixed colors, or sometimes just a single color; nonhierarchical, mathematically regular compositions, often based on a grid; the reduction to pure self-referential form, emptied of all external references; and an anonymous surface appearance, without any gestural inflection. As a result of these formal attributes, this art has also been referred to as ABC art, Cool art, Imageless Pop, Literalist art, Object art, and Primary Structure art. Minimalist art shares Pop art’s rejection of the artistic subjectivity and heroic gesture of Abstract Expressionism. In Minimal art what is important is the phenomenological basis of the viewer’s experience, how he or she perceives the internal relationships among the parts of the work and of the parts to the whole, as in the gestalt aspect of Morris’s sculpture. The repetition of forms in Minimalist sculpture serves to emphasize the subtle differences in the perception of those forms in space and time as the spectator’s viewpoint shifts in time and space.