This chapter employs hypothetical reasoning to explore Peirce’s idea of metaphor, even though the author never systematically studied the topic and left only fleeting references on the matter. The chapter first aims to illustrate Peirce’s classification of hypoicons, which includes metaphors, images, and diagrams, and outlines metaphor as a symbol where the iconic component prevails. It then investigates the factor differentiating metaphors from images and diagrams, suggesting that it can be found in their abstractness, as metaphors represent the most mature iconic form of synthesis (Thirdness). The chapter also examines the cognitive function of metaphors, arguing that they are products of abductive reasoning. Furthermore, it emphasizes the relevance of cultural context in the creation and interpretation of metaphors, concluding that it is impossible to abstractly define the “concept of metaphor”. Finally, it discusses the relationship between metaphors and scientific knowledge, illustrating that both are produced by abductive reasoning, and highlights how metaphors can contribute to the development of scientific understanding.