This contribution introduces the special issue, which contains a selection of the lectures delivered by key-note speakers during the Summer School organized by the editors in August, 2013, at the behest of the Section of Ethics & Practical Philosophy of the Dutch Research School of Philosophy (OZSW).

This article puts forward the claim that private law, and especially contract and tort, is the area of law that most clearly shows how law depends on social interactions. Taking its cue from Lon Fuller, interactional law is presented as a form of law that depends on informal social practices. Using tort and contract cases, it is argued that this implies that law is in open connection to moral norms and values, and that law cannot be understood without taking into account people’s everyday reciprocal expectancies.

Rawls’s ’idealized’ notion of reciprocity is compared with the ’real-life’ concept of reciprocity as it has been developed in social scientific theory. The two perspectives appear to differ significantly as concerns dimensions related to equality, human motivation, the temporal aspects of reciprocity, and the supposed mental origin of reciprocity. Whereas norms of obligation and feelings of moral indebtedness are constitutive for reciprocity in real-life encounters, equality, freedom and rationality are the basis for reciprocity in the hypothetical world of the ’conjectural account’. Rather than being fundamentally incompatible, the idealized and the real-life perspectives on reciprocity seem to apply to different spheres of social life, the first requiring greater formality and universality than the second, which allows for more variation and particularities.

Reciprocity seems to figure as a self-evident normative foundation of legal orders. Yet a clear understanding of the often opaque role that reciprocity plays in this regard demands drawing a conceptual distinction. This article views reciprocity as a social morality of duties, in opposition to mutuality, which concerns a legal morality of rights. In everyday life these two broad categories of human interaction interfere in a dynamic way. They need to be brought into an appropriate balance in legal orders, for the sake of justice. The practical relevance of this conceptual distinction is clarified by the debate about justice between present and future generations. I argue that this debate should be viewed as a debate about the terms of reciprocity rather than relations of mutuality. Acknowledging the deeply reciprocal nature of the relations between past, present and future generations would lead to a more convincing moral theory about intergenerational justice.

Reciprocity may serve to explain or to justify law. In its latter capacity, which is the topic of this article, reciprocity is commonly turned into a highly idealized notion, as either a balance between two free and equal parties or as the possibility of communication tout court. Both ideals lack empirical reference. If sociological and anthropological literature on forms of exchange is taken into account, it should be acknowledged that reciprocal relations are easy to destabilize. The dynamics of exchange invites exclusion and inequality. For this reason reciprocity should not be presupposed as the normative underpinning of law; instead, law should be presupposed in order to turn reciprocity into a desirable ideal.