This article enquires into the origins of the historiographical notion of double truth, a prominent and controversial category in the modern study of medieval philosophy. I believe that these origins are to be found in a short text by Jacob Thomasius from 1663, entitled De duplici & contradictoria veritate, which stands as a very early and highly original example of a history of double truth. I propose a detailed analysis of this document in order to shed light on the mechanisms (...) that transformed duplex veritas from a keyword in Thomasius’s Protestant milieu into a historiographical category. As I show, the De duplici & contradictoria veritate provides a historical legitimation of Thomasius’s own brand of Lutheran Aristotelianism. It does so in a highly ambiguous fashion, namely by bringing together the Lutheran theologian and proponent of double truth Daniel Hofmann with anonymous medieval “Averroists”. I venture an explanation for Thomasius’s line of action by uncovering two of his implicit sources. (shrink)