In current literature, metaphor is treated as either an instance of implicit comparison or as a nonliteral class-inclusion statement. I will argue that, contrary to these positions, the notions of comparison and class-inclusion are not mutually exclusive in character but rather complementary cognitive concepts which entail one another. While initially using the semantic distinction between literal and figurative language, I will argue in the course of this article that metaphor is a matter of extraordinary rather than ordinary language and that it reflects linguistic pragmatics rather than semantics. The most prominent reasons for resorting to the extraordinary use of language may be found in education, where metaphor serves a heuristic function in the interaction between teacher and student, and in scientific activities, when researchers have at their disposal only a restricted dictionary to describe new phenomena. Executive function, flashbulb memory, and the firing of neurons are examples from cognitive psychology and neuroscience that denominate phenomena that might otherwise not have been adequately expressed. I will conclude that metaphors are both comparisons as well as class-inclusion statements and that these tropes fulfill not only a heuristic but also an epistemic function in as much as they render comprehensible the acquisition of radically new knowledge.