In this article, we look at the metaphors of “mirror” and “light” in medieval vernacular literature to examine the influence of their semantics on the conceptualization of cognition. We argue that “mirror” and “light” are traditional means to express and to reflect cognitive processes. Speaking metaphorically is thus intimately related to understanding concepts in general but also allows the shaping as well as the transmission of concepts. In support of our argument, we will, in the second part of this paper, carefully consider David von Augsburg’s Spiegel der Tugend ( Mirror of Virtue), which blends the metaphors “mirror” and “light” conceptually.