Robert Heinlein’s classic 1961 sci-fi novel Stranger in a Strange Land includes a passage I’ve often thought of as a parable for scientific skepticism.

Understanding the fallibility of eyewitness testimony, Heinlein imagines a special class of “Fair Witnesses” — licensed professionals trained to observe accurately and give legally admissible testimony. In one scene, cantankerous patriarch Jubal Harshaw demonstrates that one of his staffers is a certified Fair Witness:

“Anne!” Anne was seated on the springboard; she turned her head. Jubal called out, “That new house on the far hilltop — can you see what color they’ve painted it?” Anne looked in the direction in which Jubal was pointing and answered, “It’s white on this side.”

This answer has echoed for me ever since. Anne states the evidence she has, and specifies the limits to her knowledge. As Jubal explains, “it doesn’t even occur to her to infer that the other side is probably white too. All the King’s horses and all the King’s men couldn’t force her to commit herself as to the far side . . . unless she herself went around to the other side and looked.”

True-life scientists and skeptical investigators must often (tentatively, provisionally!) piece together imperfect clues. Nonetheless, Heinlein’s fictional Fair Witnesses anticipated central commitments of modern skepticism:

Primacy of empirical evidence over armchair reasoning; Obligation to accurately state the limits of the available evidence; Refusal to reach conclusions prior to investigation.

I submit that this is the heart of skeptical practice: walking up Heinlein’s hill.

The Burden of Proof

Arguing about the burden of proof is one of skepticism’s great clichés. It’s common for skeptics to have to state the obvious: the world is not obligated to accept your idiosyncratic speculations. If you want folks to believe Barack Obama is a reptile from outer space, it’s up to you to explain why we should think that.

Just as common is the attempt to toss that burden of proof, like a hot potato, right back to skeptics. “Absence of evidence is not evidence of absence,” proponents insist. “If skeptics want to say Bigfoot doesn’t exist, they should get off their asses and prove it.” Skeptics rightly reject this rhetorical tactic — but it contains an important truth:

Doubt is cheap. Finding out is hard.

Incredulity requires no training, no knowledge, no connection to reality. By itself, doubt does nothing to advance knowledge. Even Occam’s celebrated razor is just a betting strategy. Parsimony tells us which proposed explanations to investigate first; it does not tell us which explanations are true. (Often nature is simple and elegant, but sometimes it’s a Rube Goldberg contraption. I’m reminded of the absurdly complicated life-cycles of many parasites, such as this nightmarish thing described by Brian Dunning.)

For these reasons, science-based skeptics should voluntarily take up their own burden of proof. After all, the goal of the skeptical project is not to stonewall weird ideas, but to find out what’s true.

Climbing Heinlein’s Hill

Philosopher Massimo Pigliucci makes this point in a Skeptically Speaking interview, citing examples drawn from Ufology — examples in which skeptics screwed up.

I think that a crucial aspect of being skeptical, of engaging in critical thinking, is not the idea that you reject claims because they seem absurd. That’s not being a skeptic, that’s just being a cynic. It’s just denying things for the sake of denying it. The idea of skepticism is that you inquire — that you do the work.

Although close skeptical examination of claims of extraterrestrial visitation has often revealed prosaic explanations, Pigliucci warns that the “tendency in certain skeptics quarters to just dismiss things out of hand without actually figuring out what those people saw” is a recipe for bogus pseudo-explanations.

You cannot just sit down at your computer and somebody calls you up and says, “A bunch of people have seen a UFO. What do you think it is?” — “Oh, it’s a meteor.” Well, no. You can’t just make it up. You have to do the work. Was there in fact a large meteor that night that was tracked by astronomers or by radar that fits the characteristics of the alleged UFO? … Being a skeptic, it doesn’t mean you can get lazy. You have to get your butt off your chair…and do the actual investigation.

Nor is Pigliucci’s point diminished by Steve Novella’s defense of “armchair skeptics.” As Novella clarifies, his definition of armchair skepticism is “rigorous analysis or labor-intensive archival research” which “in no way excuses superficial or sloppy analysis. Skeptics especially have to avoid that, given the public and critical nature of our endeavors.”

Whether by experiment, observation, or historical scholarship, active investigation is skepticism’s bedrock. From Houdini to James Randi, from Joe Nickell to newer practitioners like MonsterTalk‘s Blake Smith, scientific skepticism has always been defined by a willingness to do the work.

(For those who wish to contribute to skepticism’s primary literature, I recommend Benjamin Radford’s recent book Scientific Paranormal Investigation. It’s packed with good advice, and contains a hidden treasure trove: 14 mini-essays offering research lessons from investigators like Martin Gardner, Jim Underdown, and Massimo Polidoro. There are even a few thoughts from a relatively junior investigator named Loxton.)

Critical Thinking v. Science

Speaking from evidence implies making fewer assertions (as I argued here, here, and here). That’s to the good, but it feels restrictive. What about critical thinking? Science isn’t everything, right?

Like parsimony, the wider critical thinking toolset helps us to evaluate evidence and identify gaps in that evidence — but it is not a substitute for evidence. One great lesson of philosophical history is that reason is not, by itself, an adequate window into the natural world. Few would argue that Plato was a lesser mind than Galileo, but Galileo had more than just a telescope to his advantage: he tested his ideas. As Carl Sagan’s The Demon-Haunted World paraphrased physicist Robert W. Wood,

The difference between physics and metaphysics…is not that the practitioners of one are smarter than the practitioners of the other. The difference is that the metaphysicist has no laboratory.

Nor do “skeptics” fair well when doubt is divorced from evidence. Climate science denial, the 9/11 “truth” movement, Intelligent Design, vaccine fears — all rest on feral forms of critical thinking. Our internal bullshit detectors are like any other human tool: they can be misused, and they can break.

As Indie Skeptics blogger Jeff Wagg put it to me during my recent Virtual Drinking Skeptically guest spot, on many mainstream scientific topics (such as global warming) “there are a lot of flags that skeptics can pick up on and say, ‘Hey this doesn’t look real.'” I know what he means. That was my own reaction when I first heard the crazy-sounding claims of modern physics. I was sure that stuff had to be bogus. Quantum mechanics especially sounded like illogical gibberish to me — but reality doesn’t care how stupid it sounds. Personal incredulity is irrelevant. At the end of the day, science trumps everything.

Which brings us to the sticky bit. What, if anything, can intellectually honest skeptics say when no investigation is possible? But that is a post for another day….