This chapter proposes that thought experiments are a cognitive apparatus and situates this view among contemporary accounts of thought experiment. I set forward the project of the book, which is to (1) propose a new account of thought experiments as a method and (2) trace the historical foundations of the term and concept of “thought experiment” from Kant through Ørsted to Kierkegaard. I define “cognition” [Erkenntnis] for Kant as a synthesis of concepts with intuitions and propose that Kierkegaard, like Kant and Ørsted, views thought experiments as useful for achieving cognitions. I introduce the term Tanke-experiment in Kierkegaard and suggest why it has been little emphasized by Kierkegaard scholars and remains widely unacknowledged in contemporary descriptions of the history of thought experiment.