In the mid 1950's Colin Rowe and Robert Slutsky wrote a treatise comparing literal transparency with what they called (after Gyorgy Kepes) phenomenal transparency. Literal transparency referred to the effect sought by architects internationally of glass architecture, luminous, weightless buildings which proudly displayed their contents in an effort to lay bare the flawless workings of an enlightened democratic society. The thinking was: if the workings were exposed, then they might live up to their audience. Phenomenal transparency, on the other hand, was a painterly quality, evolved from cubism, which celebrated instead the visual and spatial effect of ambiguous space. Transparency, or the ability to see into complex space was achieved by the overlapping of planes and volumes and the superimposition of different volumes tending to occupy the same space.
Ultimately, the theory was not completely coherent. Although the essay was widely studied in academic circles, consensus as to its true meaning was never reached. It did, however, cause a considerable rift in the different directions pursued by architects at the time and raised convincing questions about materiality and spatial conception in the architecture that was to follow.