Robert Morris provides a complex, multi-referential discussion of contemporary sculpture; that is sculpture contemporary to 1966. He relates sculptural practice of the late 1960's to the performative work of John Cage, and marks sculpture as separate, and even hostile towards the practice of painting. Morris states that one key difference between the two practices is that painting grappled with illusionism for the half century previous to 1966, whereas he sees illusionism as irrelevant to sculptural practice; he differentiates replication (which sculpture does attempt), from illusionism. Morris sees Vladmir Tatlin as a pioneer who freed sculpture from the need to attempt representation and lists a lineage of sculptors in this tradition including Naum Gabo, Antoine Pevsner, and Georges Vantongerloo. He states that the relief is irrelevant, stating that "an object hung on the wall does not confront gravity; it timidly resists it"(Morris, 43). He goes on to discuss the role of various elements in sculpture, including colour, light, and most importantly, geometric shape.