Michael Shermer is a professional skeptic. He is the publisher of Skeptic magazine, the director of the Skeptics Society, and the author of Why People Believe Weird Things (1997) and How We Believe: The Search for God in an Age of Science (2000). Finally, he has a regular column in Scientific American magazine; the column is called "Skeptic."

Being a professional skeptic may sound like a satisfying job. You get to expose the follies of the credulous and the tricks of the hoaxter, to which you are of course immune. Alas, not everyone is cut out for this line of work. As Shermer observes in How We Believe, "To focus the narrow and intense beam of scientific light into this often dark and murky corner of the human condition can be blinding at first. As I have discovered in the course of conducting this empirical study, to most folks there is something mildly unsettling about being asked personal and penetrating questions about their most deeply held and cherished beliefs." Ah, those "folks." We know them, don't we—we see them standing in line ahead of us at the supermarket.

But there's a downside to the skeptic's job. Its demands are relentless. You can't just be skeptical some of the time. No, to live up to the job description, you must shine that "narrow and intense beam" into every nook and cranny, nor are you ever permitted to turn the switch off for a while—unless, that is, you are going to cheat, and practice selective skepticism.

And of course that is what most skeptics do. Consider for example Shermer's most recent Scientific American column, titled "The Gradual Illumination of the Mind." A subtitle proposes that "The advance of science, not the demotion of religion, will best counter the influence of creationism." Shermer ...