I argue that Kierkegaard has an account of thought experiment. While his contemporary Ørsted’s contributions to the early history of the concept of ‘thought experiment’ have been recently acknowledged, Kierkegaard’s contributions remain largely unrecognized. I argue that Kierkegaard’s method of ‘imaginary construction’ [Tanke-Experiment] aims at identifying underlying invariants in objects of experience. I outline similarities between Ørsted’s pursuit of invariants in the sciences and Kierkegaard’s fictional variations in Repetition. One implication is that Kierkegaard’s view is more scientific and methodological than (...) is standardly thought by Kierkegaard scholars, who more commonly treat imaginary construction as a literary device. A further implication is that Kierkegaard, like Ørsted, is interested in the success or failure of mental acts, rather than (or in addition to) practical action, as is more standardly associated with Kierkegaard. One original development, beyond what Kierkegaard inherits from Ørsted, is the role of thought experiments as exceptions. An exception is a case that falls outside a rule without breaking it. Exceptions can neither establish a rule nor refute its necessity; however, they turn attention to relevant principles and further determine their content. I highlight similarities between Ørsted’s account of thought experiments and Kierkegaard’s as a method of variation. (shrink)