Theories of metaphor comprehension that rely on category assignment based on common characteristics (Keysar & Glucksberg, 1992), a comparison between characteristics or relationships of source and target (Chiappe & Kennedy, 2001), or a mapping of characteristics or relationships from source to target (Gentner & Bowdle, 2001) are inherently circular, since these comparisons, mappings, or categories usually make sense only after the underlying metaphor has already been understood. This inherent circularity is avoided by approaches such as conceptual metaphor theory (Lakoff & Johnson, 1980) and conceptual blending theory (Fauconnier & Turner, 1998) that seek to explain metaphors in terms of underlying cognitive concepts or schemas.