Abstract:  Since Aristotle, many writers have treated metaphors and similes as equals: any metaphor can be paraphrased as a simile, and vice-versa. This property of metaphors is the basis for psycholinguistic comparison theories of metaphor comprehension. However, if metaphors cannot always be paraphrased as similes, then comparison theories must be abandoned. The different forms of a metaphor—the comparison and categorical forms—have different referents. In comparison form, the metaphor vehicle refers to the literal concept, e.g. ‘in my lawyer is like a shark’, the term ‘shark’ refers to the literal fish. In categorical form, ‘my lawyer is a shark’, ‘shark’ refers to an abstract (metaphorical) category of predatory creatures. This difference in reference makes it possible for a metaphor and its corresponding simile to differ (a) in interpretability and (b) in meaning. Because a metaphor cannot always be understood in terms of its corresponding simile, we conclude that comparison theories of metaphor are fundamentally flawed.