ORIGINAL ARTICLE BMost Reasonable for Humanity^: Legitimation Beyond the State Alessandro Ferrara 1 # Springer Nature Switzerland AG 2019 Abstract Legal and political philosophers of a normative bent face an uphill struggle in keeping themes of global justice and cosmopolitan governance, at the forefront of their disciplinary debate, given the perceived urgency of confronting, at the domestic level, the populist upsurge in mature democracies and Bdemocratizing societies^ alike. In this paper, these two levels of analysis— national and transnational—mutually enrich one another through a reflection on the ground of legitimacy. In the first section (BPerfectionism Redux^), (a) neo-perfectionist approaches to the legitimation of transnational authority (rooted in Kantian or Hegelian notions, or in some natural law conception of human rights) and (b) public reason approaches rooted in the paradigm of Bpolitical liberalism^ will be contrasted. In the second section (BFrom Balance to Separation of Powers^), a non-perfectionist and normative conception of the legitimacy of transnational authorities will be derived from Rawls’ s Bliberal principle of legitimacy^ (renamed Blegitimation by constitution by F. Michelman) and the difference with the application of the same principle at the domestic level will be elucidated. In the third section (BLegitimacy and the Flourishing of Humanity: Buchanan and Keohane on Global Institutions^), on the basis of such conception, one of the most complete and influential approaches to the legitimacy of transnational authorities— i.e., the BComplex Standard of Legitimacy^ expounded by A. Buchanan and R. Keohane in BThe Legitimacy of Global Governance Institutions^—will be critically assessed. Keywords Humanity . Rawls . Legitimacy . Public reason . Global governance The year 1989 brought about a major dislocation in world politics: the collapse of the Cold War bi- imperial order and the rise of a multi-polar world fraught with resurging nationalisms and explosive religious divides. It also caused a major realignment of the debate in all the disciplines that reflect on politics and law. Starting with the 1995 bicentennial of Kant’ s BPerpetual Peace,^ a body of scholarship has been growing that has taken up in earnest a question left up for utopian speculation during the past two millennia: what is a just world? Political philosophers of a normative bent, who previously had addressed justice on the scale of a national society, now Jus Cogens https://doi.org/10.1007/s42439-019-00001-1 * Alessandro Ferrara Alessandro.Ferrara@uniroma2.it 1 University of Rome Tor Vergata, Rome, Italy