Sentence:  In the Analytical phase of their Cubism , Braque and Picasso had not only had to minimize three-dimensionality simply in order to preserve it ; they had also had to generalize it - to the point , finally , where the illusion of depth and relief became abstracted from specific three-dimensional entities and was rendered largely as the <WSD>illusion</WSD> of depth and relief as such : as a disembodied attribute and expropriated property detached from everything not itself . 
Meaning of the word marked with <WSD> tags:  an erroneous mental representation