565 VIVID REPRESENTATIONS E. Davis, June 1991 This paper criticizes the widespread idea that knowledge bases in AI systems should be complete and that representations should be "model-like." The arguments in favor of such representations are less cogent and more ambiguous than they appear at first. Levesque's suggestion that representations should be "vivid" is extremely restrictive, particularly in its uniform imposition of a closed-world assumption. Spatial representations that are adequate for reasoning about a wide range of physical phenomena must ultimately either use complex symbolic reasoning or deal with partial and imperfect approximations. Requiring that temporal representations be fully detailed simulations will often be extremely inefficient. Finally, a flexible intelligent system must necessarily deal with partial information of all kinds, and the techniques for carrying out reasoning about partial information using complete representations are very limited in their application.