People perceive patterns in representations, patterns that may nothave been initially intended. This phenomenon of emergence is deemed toplay an important role in design. Computer based design assistants canand should support this human perceptual ability, using patternrecognition to anticipate human designersi perception of emergent shapesand supporting the subsequent manipulation of and reasoning with theseshapes as part of the design. Freehand drawing programs with gesturerecognition are well positioned to implement shape emergence. Supportfor emergent shapes in the Back of an Envelope system is described.