A fine little book. Jürgen Habermas and Joseph Cardinal Ratzinger (later Benedict XVI) met in Munich in 2004 to discuss "the pre-political moral foundations of a free state." Roughly translated, this means they were discussing whether a democratic society requires religion. Their presentations are collected in this book. Habermas's answer to the question is a cautious no; Ratzinger's is a cautious yes. No surprises there. Both, however, argue that religion must be allowed to play a role in the democratic, pluralistic, and (ideally) rational public sphere. Here follows my somewhat free interpretation of their remarks.
Habermas concedes that the quest for rationality poses a difficulty for a free society. The Enlightenment dream of an entirely rational (and thus free) secular society turns out to be problematic. For the truly free state cannot compel its citizens to be rational, and furthermore, rationality itself is based on prerational commitments. However, Habermas suggests that this problem fades if we see rationality as a procedural and open-ended rather than a substantive and absolute affair. Rationality emerges when all aspects of the state are under the rule of law and all constituencies in the state are free to deliberate together on the law. The results of this communicative rationality may not be perfect, but they are by definition universally authoritative, and members of the state find freedom in the rationality of the procedure. Habermas then argues that this form of communicative rationality must include, by definition, religious believers. The religious person cannot claim singular authority in the state because he relies on revelation, which is not universally accessible, for truth; at the same time, however, the secular state cannot legitimately exclude religious insight from the discussion, for all reasonable people ultimately derive their beliefs from semiprivate sources. Priests must not dictate, but neither may philosophers; neither has a monopoly on reason in the modern world. Reason only happens when everyone can come together, when every source of wisdom can contribute to the common wisdom.
Ratzinger points out what I see as a significant weakness in this model: the modern world is not limited to the West. Yet since the middle of the twentieth century, most of us in the West have claimed that certain of our values are universally valid and accessible to reason -- human rights. On a Habermasian account, that claim is only true if everyone in the world is participating in a constitutional state. Obviously, no such global, constitutional, deliberative state exists. And while broad agreement exists about certain human rights, many cultures disagree significantly about the specifics. Ratzinger argues that we are therefore forced to make claims about substantive rationality (or absolute private revelation) after all, or else lapse into agnosticism about international morality: "the rational or ethical or religious formula that would embrace the whole world and unite all persons does not exist; or, at least, it is unattainable at the present moment" (76). The upshot? Ratzinger wants us to recognize our limitations in both reason and religion, both within the West and in our relations with other cultures. He wants "an attempt at a polyphonic relatedness [...:] so that a universal process of purifications (in the plural!) can proceed. Ultimately, the essential values and norms that are in some way known or sensed by all men will take on a new brightness in such a process, so that that which holds the world together can once again become an effective force in mankind" (79-80). This is remarkably close to Habermas's position.
The key difference between the two men, I think, is that Ratzinger thinks we must often forge ahead and act on our commitments even in the absence of the circumstances making for rationality. He agrees with Habermas that communicative rationality is crucial; he just doesn't think it is always possible, even -- or perhaps especially -- in the modern world.