There are four criteria for an adequate theory of human rights: universality, prescriptive determinacy, priority and completeness. Over the course of this post, I am going to focus on the first two in the cases of Rawls and Habermas, drawn from analysis provided by David Ingram. Some preliminary definitions: universality refers to an acceptance in spite of cultural allegiances, and it can be actual in the case of agreements already reached, or potential in the case of hypothetical but probably circumstances in which we could plausibly reach agreement. Prescriptive determinacy refers to the idea that such rights are not just regulative, but actually enforceable, for instance in laws within states and internationally. The notion of priority refers to the idea that basic rights provide the necessary conditions in which one is able to exercise non basic rights, and completeness refers to all categories of rights – cultural, social and economic.
There are two main types of liberal theories: cosmopolitan, in which individuals are the primary addressees of international law, and political, in which nations are the primary addressees. Habermas’s discourse ethical theory of law is an example of the first, and Rawls’s political liberal theory of the second. There are common points of overlap between the two, however. First, both depart in different ways from Kant’s liberal theory of international justice. Second, both agree that national sovereignty must be limited by respect for human rights. Third, both agree that different people should be able to interpret these rights according to their own traditions, within reason. Disagreement between the two centres upon the limits of reasonableness: Habermas affirms the importance of liberal political institutions for realising a proper system of rights, and Rawls denies this importance.
In the case of universality, Rawlsian political liberalism ‘does an admirable job at establishing a factual basis for universal human rights, [but] it does so by relinquishing prescriptive determinacy’  because it tries to make room for radically incommensurable views of such rights in working towards international consensus.
In the case of prescriptive determinacy, Habermasian discourse theory goes some way to remedying this situation by prioritising dialogue as the basis of negotiating between cross-cultural differences. The theory has practical limitations, however, as it represent an ideal goal, but this goal does seem achievable if we drop the Rawlsian notion of the incommensurability of cultures and assume that eventually all nations will modernise and move towards democracy (modernisation theory).
In the case of priority, Ingram disputes the ranking system employed by Rawls to systematise the relative priority of basic and non basic rights. Rawls argues that human rights have priority over liberal (political and civil) rights, and the latter have priority over economic, social and cultural rights. Ingram wants to argue for an alternative ranking scheme that ‘acknowledges the equal weight and complementarity of different categories of rights’ .
For a theory of human rights to be complete, Ingram argues that it must include cultural rights, which furnish the basis of group rights. Rawlsian political liberalism only acknowledges group rights in the context of illiberal, undemocratic societies. In Habermas, ‘reluctant’  allowance of the fact that group rights might realise individual rights in a liberal democracy, is not ‘reconciled with [the theory’s] own liberal individualistic assumptions’ .
Universality and Prescriptive Determinacy
In Rawls’s opinion, legitimacy can be maintained to the degree that minority groups are tolerated, dissenting groups are adequately responded to, and each group is fairly represented in a consultation hierarchy (Law of Peoples, 69). Thus, on this view, we would be able to accept as minimally just a state that did not promote socioeconomic equality, for instance, meaning that we can allow for larger differences in economic well-being, and consequently rights, in different states. As a result, the consensus required on basic human rights is considerably weakened, because we are taking into account a broad range of states from illiberal and undemocratic to liberal and democratic. This reflects a more tolerant and pluralistic attitude towards the inclusion of reasonable people in the dialogue about human rights. Indeed, it could be argued that it is in fact illiberal for one set of states to impose their own institutional structures on another set and, moreover, the former often already acknowledge the equality of illiberal hierarchical institutions e.g. churches, within the organisation of their own states.
‘In sum, Rawls’s theory of international justice follows from his desire to extend the idea of a real social contract as far as reasonably possible. This realist – or pragmatist – decision to achieve global stability by being maximally inclusive privileges toleration of minimally decent but otherwise illiberal and undemocratic states. This extension of political liberalism presumes that any international consensus on rights and economic justice will at best be rather thin and overlapping. It will be thin because the content agreed upon will perforce be very general and all encompassing. It will be overlapping because the (assumed) cultural insularity and economic self-sufficiency of distinct peoples make agreement on a thicker, more comprehensive political-economic culture virtually impossible’. [364-5]
The point about being overlapping is particularly inimical to Habermas’s position, which seeks to distinguish stable agreement based on moral trust from an unstable ‘modus Vivendi based on strategic expediency’ . Thus, when leaders of both illiberal and liberal staets fcome together to discuss human rights, individuals will not draw uponthe specific non-shareable (moral, ethical) features of their liberal doctrines, even though ‘it is precisely these doctrines that gournd their belief in the deeper truth of these rights and principles in the first place’ (Law of Peoples, 171). Such considerations of public reason do not apply to private citizens, who can appeal to members of an illiberal state by referring to non-shareable beliefs. So, ‘given reasonable pluralism among rights interpretations at the international level, Rawls’s ideal of public reason will effectively shield illiberal consultation hierarchies from officially authorised pressures to liberalise and democratise’ . This can lead to the propping up of corrupt governments by Western democracies, and may provoke extreme feelings of anger against the latter amongst minority groups victimised by such regimes. Therefore, unless the Rawlsian notion entails a deeper level of accountability – and agreement on more substantive norms and ideals – one will not know if one has reached an agreement for anything other than purely strategic reasons.
This calls for something like the Gadamerian ‘fusion of horizons’, in which our understanding of basic rights is enlarged by genuine conversation between willing, reasonable and trustworthy participants. Mutual understanding enables us to reach and refine consensus, and individualism is ‘mitigated and transformed by the ecological communalism of more spiritual traditions’ . Under Habermas’s model, legitimacy is engendered by consensus, which in turn entails a sense of what is reasonable, i.e. when it derives from inclusive conversation in which all relevant assumptions are open to criticism.
‘The disagreement between Rawls and Habermas thus largely boils down to a disagreement about reasonableness. For Habermas, reasonableness imposes an ideal demand to criticise comprehensive assumptions in open and inclusive dialogue; indeed it stems from a comprehensive philosophical demand that agreement be ceated where none exists and that it be created autonomously, through the radical questioning, if need be, of all assumptions. Rational conviction is both egalitarian and deep; for genuine dialogue is distinguished from rhetorical manipulation by being motivated solely by reasons that would be accepted as true – grounded in deeper, comprehensive philosophical theories – by persons who speak to one another as free and equal moral subjects, unhindered by material inequality or ideological coercion’.