The function of solidarity and its normative implications

Many lament that solidarity is declining, implying there is something good about it; but what is solidarity and why should we want it? Here, we defend an original functionalist re-interpretation of solidarity. Political solidarity plays a key functional role in a polity's persistence through time. Thus, we should want institutions that foster solidarity. This paper is divided into three parts. In the first, we draw on the philosophy of biology to pinpoint what counts as a proper function, in a way that is naturalistic, objective, and selective. On this aetiological account, a sharp distinction between functional needs (e.g. the pumping of blood) and functional mechanisms (e.g. the valve that pumps blood) is drawn. In the second part of the paper, we propose that solidarity should be understood as an aetiological function of society. This new conception sheds light on the widely acknowledged, yet seldom clarified connection between two common readings of solidarity: solidarity as a set of feelings of mutual kinship (its functional need), and solidarity as a set of redistributive institutions (a key functional mechanism). The third part concludes that this new functional conception of solidarity provides normative reasons to foster solidarity.