Rick Perry’s recent vocal dismissals of evolution, and his confident assertion that “God is how we got here” reflect an obvious divide in our culture. In one sense, that divide is just over the facts: Some of us believe God created human beings just as they are now, others of us don’t. But underneath this divide is a deeper one. Really divisive disagreements are typically not just over the facts. They are also about the best way to support our views of the facts. Call this a disagreement in epistemic principle. Our epistemic principles tell us what is rational to believe, what sources of information to trust. Thus while a few people may agree with Perry because they really think that the scientific evidence supports creationism, I suspect that for most people, scientific evidence (or its lack) has nothing to do with it. Their belief in creationism is instead a reflection of a deeply held epistemic principle: that, at least on some topics, scripture is a more reliable source of information than science. For others, including myself, this is never the case.
Disagreements like this give rise to an unnerving question: How do we rationally defend our most fundamental epistemic principles? Like many of the best philosophical mysteries, this a problem that can seem both unanswerable and yet extremely important to solve.
The ancient Greek skeptics were the first to show why the problem is so difficult to solve. Every one of our beliefs is produced by some method or source, be it humble (like memory) or complex (like technologically assisted science). But why think our methods, whatever they are, are trustworthy or reliable for getting at the truth? If I challenge one of your methods, you can’t just appeal to the same method to show that it is reliable. That would be circular. And appealing to another method won’t help either — for unless that method can be shown to be reliable, using it to determine the reliability of the first method answers nothing. So you end up either continuing on in the same vein — pointlessly citing reasons for methods and methods for reasons forever — or arguing in circles, or granting that your method is groundless. Any way you go, it seems you must admit you can give no reason for trusting your methods, and hence can give no reason to defend your most fundamental epistemic principles.
This skeptical argument is disturbing because it seems to suggest that in the end, all “rational” explanations end up grounding out on something arbitrary. It all just comes down to what you happen to believe, what you feel in your gut, your faith. Human beings have historically found this to be a very seductive idea, in part because it is liberating. It levels the playing field, intellectually speaking. After all, if all reasons are grounded on something arbitrary, then no one’s principles rest on any firmer foundation than anyone else’s. It seems to give us the freedom to go with any epistemic principle we choose.
The methods of observation and experiment have roots in our natural instincts.
Many people who are committed to the core epistemic principles of science — say, that observation and experiment should be trusted over appeals to scripture — are inclined to shrug this worry off. Why, they ask, should I care about convincing people who don’t understand the obvious fact that science is always the better method for knowing about matters like the origin of life on this planet? (This is a question also raised in the recent debate on naturalism in The Stone.) Again, epistemic principles tell us what is rational. So anyone who doubts my basic epistemic principles is going to appear to me as someone who doubts the rules of rationality. So, why should I care about what they think? It’s not as if they’ll be able to recognize my (good) reasons anyway, and to me, their “reasons” will not be legitimate.
But what counts as “legitimate”? There’s the rub. A legitimate challenge is presumably a rational challenge. Disagreements over epistemic principles are disagreements over which methods and sources to trust. And there we have the problem. We can’t decide on what counts as a legitimate reason to doubt my epistemic principles unless we’ve already settled on our principles—and that is the very issue in question. The problem that skepticism about reason raises is not about whether I have good evidence by my principles for my principles. Presumably I do. The problem is whether I can give a more objective defense of them. That is, whether I can give reasons for them that can be appreciated from what Hume called a “common point of view” — reasons that can “move some universal principle of the human frame, and touch a string, to which all mankind have an accord and symphony.”
I think that we ignore this problem — the problem of defending our epistemic principles from a common point of view — at our peril. It is not that I think we should come up with a list of bullet-points to convince people to employ scientific reason in public discourse. That would be a waste of time. Nor is my point that it is politically stupid to dismiss other people’s viewpoints in a democratic society. (Although it is. You don’t help your message by displaying a haughty indifference to others’ challenges.) My point is that defending some of our epistemic principles, our faith in reason, is required by some of our other principles. Hume’s point, in alluding to what he also sometimes called “the principle of humanity” was that the ideal of civility requires us to find common currency with those with whom we must discuss practical matters. More recent political philosophers like Rawls and Habermas have seen this ideal as a key component of a functioning liberal democracy. In this view, democracies aren’t simply organizing a struggle for power between competing interests; democratic politics isn’t war by other means. Democracies are, or should be, spaces of reasons.
So one reason we should take the project of defending our epistemic principles seriously is that the ideal of civility demands it. But there is also another, even deeper, reason. We need to justify our epistemic principles from a common point of view because we need shared epistemic principles in order to even have a common point of view. Without a common background of standards against which we measure what counts as a reliable source of information, or a reliable method of inquiry, and what doesn’t, we won’t be able to agree on the facts, let alone values. Indeed, this is precisely the situation we seem to be headed towards in the United States. We live isolated in our separate bubbles of information culled from sources that only reinforce our prejudices and never challenge our basic assumptions. No wonder that — as in the debates over evolution, or what to include in textbooks illustrate — we so often fail to reach agreement over the history and physical structure of the world itself. No wonder joint action grinds to a halt. When you can’t agree on your principles of evidence and rationality, you can’t agree on the facts. And if you can’t agree on the facts, you can hardly agree on what to do in the face of the facts.
Put simply, we need an epistemic common currency because we often have to decide, jointly, what to do in the face of disagreement. Sometimes we can accomplish this, in a democratic society, by voting. But we can’t decide every issue that way, and we certainly can’t decide on our epistemic principles — which methods and sources are actually rationally worthy of trust — by voting. We need some forms of common currency before we get to the voting booth. And that is one reason we need to resist skepticism about reason: we need to be able to give reasons for why some standards of reasons — some epistemic principles — should be part of that currency and some not.
Yet this very fact — the fact that a civil democratic society requires a common currency of shared epistemic principles — should give us hope that we can answer the skeptical challenge. Even if, as the skeptic says, we can’t defend the truth of our principles without circularity, we might still be able to show that some are better than others. Observation and experiment, for example, aren’t just good because they are reliable means to the truth. They are valuable because almost everyone can appeal to them. They have roots in our natural instincts, as Hume might have said. If so, then perhaps we can hope to give reasons for our epistemic principles. Such reasons will be “merely” practical, but reasons — reasons for reason, as it were — all the same.
 Philosophers typically take ancient skeptical arguments to challenge the possibility of knowledge. I don’t think they do. What they challenge is the possibility of ever defending and articulating our knowledge to those who see things differently.
 Enquiry Concerning the Principles of Morals in “Enquires Concerning Human Understanding and Concerning the Principles of Morals,” ed. I. A. Selby-Brigge. 3rd ed. Revised by P. H. Nidditch. (Oxford: Oxford University Press, 1975). IX, 1, pp. 272-273.