This chapter argues that the cognitive basis of thought experimenting lies in the mundane cognitive capacity for mental modeling. Wherever one stands on the issues of how a thought experiment is executed and how it provides novel insights into the real world, clearly thought experiments utilize the human capacity for imaginative thinking. The general hypothesis is that thought experimenting is a species of reasoning rooted in the ability to imagine, anticipate, visualize, and re-experience from memory. When a thought experiment is successful it can provide novel empirical data in the sense that although they are contained in current representations, the means to access them were not available until someone figured out how to conduct the thought experiment. Accounting for simulative reasoning about physical systems, and thought experimenting in science in particular, requires more kinds of model manipulation than logical reasoning requires.