The history of thought experiments is now gaining a great deal of attention, and this is due to the renewed interest of philosophers on the subject. This paper inquires into the history of the philosophy of thought experiments. We name the period to be examined in this paper the "forerun." Its main stakeholders are Georg C. Lichtenberg, Novalis, and Immanuel Kant. We will present and discuss the work of each of them in order to characterize the period, and then reveal parallels and lessons that apply to more recently proposed accounts of thought experiments.