stephens-2009uec

We present evidence from videotape transcripts for the productive use of extreme case reasoning by both scientifically trained experts and students. Extreme cases appear to be a powerful method for making inferences about physical systems but the origin of their power is difficult to explain. Spontaneous gestures and other imagery indicators provide evidence that they can involve the use of imagery in mental simulations as a possible source of power. The study identifies a reasoning process that can contribute to theory construction in scientists, and suggests that it may involve imagery and simulation in a central way. It attempts to describe an active nonformal reasoning process that students can do with some scaffolding, and outlines some of its strengths and limitations.