 The question of what role the human mind plays in moral behaviour—or the study of moral psychology—has been a fruitful area of research in medieval philosophy since at least the early to mid-1990s. Since then scholars have done much to illuminate medieval contributions to such perennial topics as the freedom of the will, the problem of moral weakness, and what role, if any, the emotions and the moral virtues play in the achievement of happiness (e.g., Kent 1995, Saarinen 1994, Dumont 2000, Eardley 2006, Hoffmann 2007, and Osborne 2014). Similarly, metaethical theories about the foundations of morality that were prominent during the medieval period such as natural law theory—particularly in its Thomistic and Scotistic variants—continue to receive robust scholarly attention (e.g., Porter 2005, Möhle 2003, Lisska 2012, Sweeney 2012, and Cross 2012). Comparatively less consideration, however, has been devoted to what was believed to link the psychological to the metaethical: the mental habit or act of conscience (and its sister-concept of synderesis), though interest in the subject has recently seen a modest resurgence (e.g., Hoffmann 2012, Eardley 2013, and Dougherty 2018).