John Thompson describes how Martin Luther and John Calvin treated conscience. For Luther, natural conscience is beset by knowing that a person can never meet the rigorous requirements of the law. Faith can relieve a person’s downtrodden conscience, which would otherwise condemn him. Once a person accepts the favor of God that flows solely from trusting him, his conscience is liberated. He knows he can do nothing himself to merit that favor. His conscience is freed “to trust God’s promise of mercy and forgiveness.” The highest functioning conscience for Luther, then, is the one that does not depend on its own goodness or perfection. Calvin teaches that, though a person’s conscience is a natural faculty, it is marred and affected by the fall. Once a person is saved, however, his conscience is transformed so that he desires to obey the will of God found in the law. This is true even though adherence to the law will not add in the least to his salvation. For this reason, Calvin created a catechism to train and chasten Genevan Christians’ consciences. Calvin also helped to establish the Geneva consistory, which was less a disciplinary body, and rather “a school for consciences.”

This chapter deals with the question of how the established order of salvation, expressed in terms of the processus iustificationis, can be reliable without in some sense being necessary – and hence violating the divine freedom. This debate became increasingly important in late thirteenth-century theology, and was generally framed in terms of a dialectic between the ‘two powers’ of God. God’s ordained power designated the realm of the actual which, though reliable and grounded in God’s promises, was contingent. God’s absolute power referred to a world of possibilities which subverted the established order of salvation – such as God’s ability to accept someone without a created habit of grace. The chapter opens by considering how medieval theology used the notion of God’s ordained power (potentia ordinata) to explore the self-limitation of God, simultaneously establishing the provisionality and reliability of the established order of salvation. It then moves on to consider criticisms of the logical necessity of certain aspects of this established order, particularly those developed by Duns Scotus, William of Ockham, and representatives of the via moderna,such as Gabriel Biel.

The concept of merit plays an important role in the medieval discussion of justification. Although it was widely considered to be unacceptable to allow that human beings could be said to earn or deserve their justification, in the strict sense of the terms, the concept of merit was developed extensively to allow a strict concept of merit (usually referred to as ‘condign merit’) to be distinguished from a weaker sense of merit (usually referred to as ‘congruous merit’). The chapter opens by considering how Augustine’s concept of merit was complexified during the Middle Ages, and the reason for this process. Particularly within Franciscan schools of theology, there was a widespread recognition of a gradation of forms of merit, including the notion of merit as a self-imposed divine obligation. This chapter explores these divergences, and notes the growing tendency on the part of writers such as Duns Scotus and William of Ockham to adopt voluntarist rather that intellectualist approaches to merit, locating the ground of merit in God’s decision to accept certain actions as meritorious. The chapter concludes by noting the continuity between these later medieval lines of thought and those associated with the Reformation – such as John Calvin’s understanding of the grounds of the merit of Christ, on which human salvation was held to be contingent.