Diagrams are of substantial benefit to WHISPER, a computer problem-solving system, In testing the stability of a "blocks world" structure and predicting the event sequences which occur as that structure collapses. WHISPER'S components include a high level reasoner which knows some qualitative aspects of Physics, a simulated parallel processing "retina" to "look at" Its diagrams, and a set of re-drawing procedures for modifying these diagrams. Diagrams enable WHISPER to work with objects of arbitrary shape, detect collisions and other motion discontinuities, discover coincidental alignments, and easily update its world model after a state change.