Robert Morris's contribution to from about 1965-7 was outstanding in its rigour, and he preferred the term Unitary Objects for the work he produced. In his Notes on Sculpture
published in the influential journal Artforum
from 1966 he attempted to define an absolute essence of sculpture in much the same way as Ad Reinhardt had done for . He insisted that sculpture was 'scale, , shape, mass'. To reveal these properties most purely, simple forms such as cubes, pyramids and regular polyhedrons should be used. He emphasised that such forms 'create strong gestalt sensations'. Gestalts are patterns or configurations where the whole has a significance greater than, and different from, any of the parts considered individually. The study of gestalts as a phenomenon of human perception began in 1910 and gave rise to Gestalt Psychology, one of the six main branches of psychology. The theory of gestalts is echoed in Morris's statement that 'Simplicity of shape does not necessarily equate with simplicity of experience. Unitary forms do not reduce relationships'. Gestalts are of course an important aspect of much Minimal Art.
This work by Morris, consisting of four large cubes of mirror glass placed at the four corners of a square, is a perfect example of a gestalt, its four essentially simple elements together producing complex and fascinating interactions with the environment in which they are placed and with the spectator who walks among them, while fully retaining their simple identity. Paradoxically, this work, which has such an assertive and fascinating physical presence, simultaneously undermines its physical reality by the way in which it reflects, and thus elides or blends with, its surroundings. This phenomenon was particularly evident when the work was placed on the front lawn of the Tate Gallery during Morris's retrospective exhibition there in 1971.
Simon Wilson, Tate Gallery: An Illustrated Companion, Tate Gallery, London, revised edition 1991, p.262