Why be reasonable? Political liberalism, moral pluralism, and deep disagreement

Political liberalism contains a commitment to public justification. The exercise of coercion on the basis of political principles is only thought to be proper if these principles are acceptable to each and every reasonable person. The fact that political liberalism restricts the constituency of public justification, i.e., the constituency of those who are owed justifications, to reasonable people is significant. I argue that, as it stands, this restriction is problematic. Specifically, political liberalism's core commitment to respect for persons as ends in themselves is in conflict with its refusal to justify their exclusion to some individuals who will be coerced. Furthermore, attempts to dispense with the need to provide justifications to the unreasonable seem to resolve that tension, but only at the cost of introducing a second defect: an impoverished and ultimately illiberal conception of the person which refuses to regard individual persons as morally autonomous. I conclude that political liberalism must justify the very criterion of individuals' exclusion from the constituency of public justification -- reasonableness -- to those who fail to live up to that standard. The justifications it offers must not loose sight of the liberal commitment to respecting individuals' moral autonomy. To that end, I argue, such justifications must be rooted in the set of reasons and beliefs which individuals can be said to be committed to. Two different kinds of unreasonableness warrant different kinds of justifications: there are those who are fundamentally unreasonable because they reject the core liberal commitment to persons as free and equal, while others merely fail to be fully reasonable when encountering deep moral disagreement in political debates, falling short of the requirement to engage with others in public reason on the basis of shared values. With respect to the former, it can be argued that a commitment to regarding their fellow citizens as free and equal is implicit in their attitude and conduct towards them. The latter individuals can be offered justifications for restraint which are rooted in the character of the very moral convictions they are tempted to draw on in public reason.