This article proposes that Calvin's ‘hardness of heart’ principle functions as a substantive limitation on political authority and the law, creating the legal space for meaningful moral pluralism. Calvin distinguished between the spiritual and civil uses of the law, as well as between the natural moral law and the civil law within the Mosaic law. He repeatedly used Jesus' concept of ‘hardness of heart’ to explain inadequacies within the Mosaic law and to articulate a general principle about the nature and limits of civil law. This approach has important implications for law and morality in contemporary contexts characterised by a degree of moral pluralism that Calvin scarcely could have anticipated.
