Ius Filiationis: A defence of Citizenship by Descent Rainer Bauböck Aristoteles famously defined a citizen as someone ‘giving judgment and holding office’ in the polity.1 Yet, this does not settle the issue since we first need to know who qualifies for holding office. And so he continues: ‘For practical purposes a citizen is defined as one of citizen birth on both his father’s and his mother’s side’.2 Times have changed. From the French Revolution, which revived ius sanguinis, until the second half of the 20th century, citizenship was mostly transmitted only from the father to the child. Today, largely as a result of international conventions against the discrimination of women, all democratic states define a citizen as one of citizen birth on either the father’s or the mother’s side. Yet ius sanguinis remains the dominant rule for acquisition of citizenship worldwide. True, in the Americas the stronger principle is ius soli, the acquisition of citizenship through birth in the territory. But even there those born abroad to citizen parents who were themselves born in the country are recognised as nationals by birth. Given this overwhelming presence of ius sanguinis in nationality law, Costica Dumbrava’s call for abandoning it is bold. Some might even say, it is quixotic, but I disagree. It is indeed time to reflect on the future of ius sanguinis and to abandon it as a doctrine linking citizenship to biological descent. Yet there are good practical and normative reasons why the principle of citizenship transmission from parents to children will remain alive and ought to be retained. Dumbrava runs three main attacks against ius sanguinis: It is tainted by its association with ethno-nationalism; it is inadequate because, in an age of artificial reproduction technologies, same sex marriage and patchwork families, biological descent no longer traces social parenthood; and it is unnecessary since its protective effects can be achieved by other means. I will accept the first and second argument with some modifications but reject the third. 1 2 Aristotle (1962), The Politics. Transl: T.A. Sinclair, revised and commentary: T. J. Saunders (ed.). London: Penguin, III. i: 169. Ibid, III.ii: 171-2, original emphasis. © The Author(s) 2018 R. Bauböck (ed.), Debating Transformations of National Citizenship, IMISCOE Research Series, https://doi.org/10.1007/978-3-319-92719-0_17 83