This chapter focuses on Maritain’s analysis of the ontological and epistemological foundations of human rights, and his wider hope for ‘practical agreement’ on the content of those rights. On the ontological front, I argue that such agreement is not forthcoming on the basis of natural teleology or eternal law. Neither of these secures assent across the world’s major religious or philosophical traditions. On the epistemological front, neither rationalism nor naturalism holds great promise. While Maritain upholds the naturalist alternative, his efforts devolve into a performative contradiction. For he hopes to rest agreement about human rights on ‘natural inclinations’, which, at the same time, he confines to the realm of the non-conceptual, non-rational and pre-conscious. This constitutes a markedly weak, even incoherent basis for agreement. The stage is set, therefore, for ‘new’ natural law theory, which proposes a non-ontological, purely rationalist foundation. I conclude that this too is an unpromising basis for agreement on rights. Instead, we need a new approach, one that privileges the deliverances of the social sciences and does not strive for universal consensus.