The present book is based on the fundamental consideration of whether it is possible to apply the complex themes of ideology and ideology critique to a historical period in which these philosophical terms did not yet exist. To this end, the author selects an episode from medieval history, namely the so-called Predestination Controversy of 840-860, to explore this question using a specially adapted catalog of criteria for ideological practices. The investigation provides the reader with a comprehensive insight into the problem of predestination itself and further offers a historical overview of the development of the concept of ideology, as well as a clearly structured model for analyzing ideological thought. The concrete application of this model is ultimately demonstrated in a detailed ideological critique of the various positions in the controversy surrounding gemina praedestinatio. The book is primarily intended for those who enjoy engaging with medieval philosophy, but it is also directed at those for whom ideology is more than just a polemical battle formula.