This paper presents a corpus-based approach to investigating the function of metaphor, specifically to the question whether the use of metaphorical language is motivated primarily by stylistic considerations or by cognitive principles. The paper focuses on concepts that can be expressed alternatively by a literal or a metaphorical linguistic expression with the same structural properties. Such expressions can be individual words (such asgraspandunderstand, which can both encode the concept UNDERSTAND), or fixed phrases (such asin the heart ofandin the center of, which can both encode the concept IN THE CENTER OF). It turns out that a comparison of the distinctive collocates of the literal and the metaphorical variant in each case provides clear evidence for the hypothesis that metaphorical language has a cognitive function.