“Reason is man’s only absolute,” Ayn Rand famously declared. Similarly, Murray Rothbard thought that reason uniquely vindicated the non-aggression principle on pain of self-contradiction, for “the preservation and furtherance of one’s life takes on the stature of an incontestable axiom” (The Ethics of Liberty, 33). Mises claimed that that the problems of social policy should be sought “in the same ways and by the same means that are at our disposal in the solution of other technical problems: by rational reflection and by examination of the given conditions. All that man is and all that raises him above the animals he owes to his reason.” (Liberalism, 7)

What do these three figures share? They believe in the consensus-generating power of human reason. In other words, they think that human reason, carefully exercised, will lead to moral agreement either on the nature of the good life, that the non-aggression principle is entailed by the universal value of life on pain of contradiction or on the principle of utility and its proper exercise.

It is sometimes said that the “Enlightenment” conception of reason was “confident” because Enlightenment thinkers believed that reason alone could solve our major social problems and give us true moral knowledge. Faith obscures, reason illuminates. Enlightenment-era liberalism was based on this optimism in unaided reason, and that optimism, in my view, filtered down into 20th century libertarianism. “Mysticism” as Rand and Mises called it, must be avoided. If only we can set aside our biases, ignorance and vice, we can all see that libertarianism or something like it (Objectivism) is the correct governing ideology.

Hayek, perhaps alone among libertarian intellectual heroes, was deeply skeptical of the power of human reason to secure agreement and knowledge. He constantly emphasized the fragmentation of knowledge – that we could never come to agree on a common scale of values or know enough to centrally plan the economy. Human reason, Hayek thought, is necessarily based in the mind understood as a classification system that is subject to evolutionary conditioning. Libertarians have criticized what we might call this “post-Enlightenment” conception of reason, fearing it leads to skepticism or relativism.

Significantly, the later Rawls agreed with Hayek – the free exercise of practical reason would lead us to disagree rather than agree about life’s most important questions, including about how to live together. I have elsewhere outlined Rawls’s view.

Gerald Gaus argues that over the last fifty years, liberal political theory has transitioned from an Enlightenment confidence in human reason to a post-Enlightenment view that recognizes the challenge of reasonable pluralism. The post-Enlightenment view still aspires to show that our diverse reasoning can lead us to converge on public principles that protect human freedom, but its aspirations are chastened. The fact of reasonable pluralism explains why many liberals have become public reason liberals, because treating others as free and equal requires admitting that the free use of practical reason leads in many different directions.

One reason I think libertarians have often allied with conservatives is that they wish to preserve a belief in an objective moral order. This is a key emphasis in Rothbardian and Randian thought. In a certain way then, American conservatives and libertarians share an ironic wish to preserve Enlightenment conceptions of reason, where reason leads to convergence on the right and the good. Reasonable pluralism seems to challenge this fact, since reasoning plainly does not lead to agreement.

I believe in reasonable pluralism and the post-Enlightenment’s more chastened conception of the ability of reason to generate unforced agreement. And I think that libertarians often seem authoritarian and ideological because they do not recognize these limits.

The point of a public reason libertarianism is that there are mutually justifiable norms that allow us to get along despite the fact that we will always disagree about matters of great import. Public reason libertarianism, a post-Enlightenment libertarianism, does not deny moral truth, but, recognizing the interminability of disputes about moral truth, attempts to justify moral order in some other, more interpersonal mode.

Due to embracing this post-Enlightenment critique of reason, I have become increasingly unsympathetic to Rothbardians and Randians who insist that reason will completely vindicate their moral and economic views. They prattle on about “axioms” that aren’t axioms at all, and claim that their incredibly controversial views are rationally undeniable. Such claims cannot withstand rational scrutiny and so prove to be poor foundations for a libertarianism that can speak to a post-Enlightenment world.

Only the dogmatist can insist that there is a faculty, REASON, which demonstrates that you are right and everyone else is wrong in a way that no one could honestly deny. Perhaps you libertarian readers believe, as I do, that the best reasoning, arguments and information show that our personal views are justified and perhaps uniquely so. But we would do well to recognize that others reasonably disagree.

Hayek and Rawls have taught us that disagreement is the natural result of living in a free society. And this fact should affect the way in which we attempt to justify a free society. Hayek and Rawls obviously disagreed about the nature of a free society but they asked the right questions, which is why I think they will matter increasingly more in libertarian political theory than Rand, Rothbard and Mises, as inspirational and important as they may be.

Many of my blog posts have been devoted to explaining the structure and ground of a public reason libertarianism. And I think that embracing it on the basis of a post-Enlightenment conception of free reasoning will have three salutary effects on the libertarian movement.

(1) We will be better able to recognize bad arguments when they come along, as we will be less likely to think that the case for a free society is settled among rational and informed persons.

(2) We will be able to set aside the cults of personality that plague the liberty movement by peeling away the charismatic veneer from figures who “get it” and have the obviously correct view that others can only deny via wickedness or stupidity.

(3) We can learn to speak to a post-Enlightenment political culture, one where diversity of belief and practice is a permanent fact of life, without seeming authoritarian and ideological.