The debates around the use of the metaphor in the social sciences reveal the tensions at work in collective perceptions of what these sciences ought to be. As a mere image or vehicle of meaning, can the metaphor go beyond its apparently legitimate role of illustration, or even become a substitute for analysis? Does the heuristic dimension of the metaphor allow us to justify these uses? By analyzing the controversy opened by A. Sokal and J. Bricmont, we try to show the difficulty of establishing clear boundaries for the legitimate use of the metaphor, and how the discussions about the metaphor focus and concentrate many other debates, both epistemological and political.