In the debate between Andrew Sullivan and Sam Harris (and in many other debates about religion) a central question often seems to be whether there is any "scientific" evidence for any of the supernatural claims religion makes. In my comments, I've made the point (somewhat implicitly) that this is the wrong question. Here I'd like to clarify this point. It seems to me that the important question is not whether secular human inquiry can confirm supernatural religious claims but whether religious claims can add anything to secular human inquiry about the natural world.
Most modern adherents of religion would say that religion can't add anything to secular human inquiry about the natural world. Only certain fundamentalists and other religious intransigents now claim that religion can compete with science or other forms of secular human inquiry in determining facts about the natural world. Religion no longer claims to have a position about issues such as evolution or whether the earth orbits the sun. Issues such as these are left to secular inquiry.
Recent attempts to measure the efficacy of anonymous prayer in healing illustrate the sort of question that might be used to establish a claim that religion can add to our understanding of the natural world. Studies about such effects were first published in reputable journals but later withdrawn. If this work could be put on a more firm foundation, it would provide evidence that religion has something to say about the natural world that is not accessible through other forms of inquiry.
On the other hand, if no such evidence is brought forward, then it seems to me that religion as a theory about the natural world is essentially impotent. One may believe it or not with no intellectual consequences either way.
Of course whether or not religion has anything to add to secular inquiry regarding the natural world, religious beliefs certainly affect how many people act. But that's an entirely different issue.