AbstractRecent scholarship has done much to uncover a continuous tradition of distinctively Reformed natural law reflection, according to which knowledge of the natural moral law, though not saving knowledge, is universally available to humanity in its fallen state and makes a stable secular order possible. A close look at Calvin's understanding of natural law, and in particular of conscience and natural human instincts, shows that Calvin himself did not expect the natural law to serve as a source of substantive action-guiding moral norms. First, Calvin held that conscience delivers information concerning the moral quality even of individual actions. But he also thought that we often blind ourselves to the deliverances of conscience. Second, he argued that our natural instincts predispose us to civic order and fair dealing insofar as these are necessary for the natural well-being or advantage of creatures such as ourselves. But he also carefully distinguished the good of advantage from the good of justice or virtue. The modern natural lawyers eroded Calvin's careful distinction between conscience as revealing our duty as duty, and instinct as guiding us towards natural advantage. They also turned away from Calvin's insistence on the moral incapacity of unredeemed humanity. The modern natural lawyers saw their task as one of developing an empirical science of human nature to guide legislation and shape international law, bracketing questions of whether this nature was fallen and in need of redemption. When Scottish Presbyterian Reformed thinkers, such as Gershom Carmichael and John Witherspoon, tried in diverse ways to restore eroded Reformed commitments to the science of human nature, about which they were otherwise so enthusiastic, they were not particularly successful. A science which could derive moral norms from an examination of human instincts, and a conscience which could deliver universal moral knowledge, proved too attractive to decline simply because of the transcendence of God or the fallenness of humankind. Those who wished to preserve an account of natural law which remained faithful to a fully robust set of Reformed theological commitments could do so only by refusing to regard the natural law as a positive source of moral knowledge.