Despite its foundational role in contract law, the term mental capacity is entirely metaphorical, and a detailed analysis of three representative judicial opinions shows that courts' explanations of the term are equally metaphorical. As such, the term mental capacity nicely illustrates the cognitivist view that abstract concepts arise through an imaginative but orderly projection from the domain of bodily and social experience. Legal Realists, including notably Felix Cohen, condemned metaphors for their supposed failure to constrain judges, but this article and other recent empirical work indicates that metaphorical thinking is indeed constrained. I accordingly suggest that thinkers such as Cohen would probably have welcomed the cognitive analysis of metaphor in law, both for its methods and for its substantively progressive disposition. (Carl S. Bjerre)