This chapter experiments with the application of the model of fashion rhythms developed in Chap. 1 to a description of the rhythms of knowledge. The notion of “trend” is defined not as a fashion industry tool but as an abstract operator that dictates rhythmic changes affecting every type of “product”—including knowledge forms. Four case studies of “epistemic fashions”—the fashions of “Social Justice”, “Ancient Knowledge”, “Sustainability”, and “Interdisciplinarity”—aim to provide the foundations of a study of how fashion governs the movement of thought traditions, cultural “obsessions” that become the object of scholarship, approaches to the environment, and manners of researching. The second part of this chapter presents the description of the abstract model derived from these analyses through the model of fashion rhythms presented in Chap. 1 . Beyond the critique of the commodification of knowledge forms, the objective of this section is to expose the semiotic mechanism of change and how fashion in every realm operates by translations and rhythms of decomplexification and recomplexification of forms that change the direction of discourses.