Some Basic Skeptical Principles
We’ve seen that skeptics knowingly risk the possibility of rejecting a truth because of the majority of falsehoods there are about the world, but skeptics do not do so arbitrarily.  Surprisingly, the reasoning a skeptic uses to come to conclusions really isn’t all that different from how most people reason, although skeptics are typically much more aware of their thinking processes than most others.  The difference is when evaluating claims that challenge fundamental or predisposed beliefs about the world.  Because of the nature of skeptical thinking discussed in Part 1 of this essay, skeptics have fewer beliefs about the world than most people (esp. True Believers).  So, skeptics are inherently conservative when it comes to beliefs and demand good reason to change or reject beliefs, or accept new beliefs.

If you’ve ever bought a new car, you know how to be skeptical.  A skeptic, though, applies the same type of skepticism when buying a used car to other claims about the world.  How does a skeptic reason through a claim?  Well, though not a step-by-step process, there are some general guidelines of thought that skeptics follow when evaluating a claim.

What follows is a list of what I think are some of the fundamental principles of skepticism.  While not intended to be a complete, comprehensive list, I’m comfortably sure that most skeptics would agree with my assessment:

The Open Mind Principle
All knowledge is tentative.

Probably the most important principle of all, OMP reminds us that since we are not omniscient, we must be aware that what we may hold true today may be found false tomorrow.  If new, verified evidence comes to light that challenges our beliefs, we must either change the beliefs or reject them outright.  Truth is never certain and steadfast faith only closes our mind to alternative possibilities.  Skeptics should never be pertinacious about beliefs, only with how those beliefs are acquired.

The Dogma Reduction Dictum
Proportion your beliefs to the evidence.

This principle comes from David Hume, one of the "founding fathers” of modern skepticism.  What this principle means is that the more evidence that backs up a claim, the greater confidence you can have that the claim is true.  On the other hand, if there is little or no evidence for a claim, you can reasonably conclude that the claim is false.

The Negative Evidence Clause
Absence of evidence is not evidence of absence

Deriving from OMP and DRD, NEC cautions us not to discount a claim just because there is no evidence to back it up.  Just as OMP implies, it could just so happen that tomorrow there is some evidence to support the claim.  However, at the same time DRD indicates that we should not hold much stock in it.  So, just as we can say a claim is true if there is enough evidence to warrant such an allowance while still being aware of OMP, so too can we provisionally say a claim is false while keeping OMP in mind.

The Subjective Experience Caveat
Anecdotes are not evidence.

People are fallible; therefore, their stories can be inaccurate, wrong, or outright lies.  This is not to say that an anecdote can never be 100% accurate, but there must be independent confirmation of the facts.  Anecdotes can be used as support for the claim but they cannot be all the evidence there is.  Anecdotes can lead us to the truth, but they are not the truth.  One of the most powerful ways a seller can promote a product is in the use of testimonials.  Endless numbers of television commercials use this method of advertisement (esp. infomercials) simply because most people trust personal evaluations instead of scientific evidence.[1]  However, ads will never show a representative sample of customer evaluations simply because showing negative opinions affect consumer opinion (and for obvious reasons).

The Believability Threshold
Extraordinary claims require extraordinary evidence.

Not all claims are worthy of skepticism.  Skeptics generally segregate claims as "mundane" or "extraordinary."  A mundane claim is one that does not challenge fundamental beliefs about the world.  For example, take the claim “This morning I woke up and went to the bathroom."  Well, from experience, we know that most people wake up during the mornings and every person "uses the bathroom," to some extent. While this claim could very possibly be false, you can reasonably conclude it is true until there is some good reason to believe otherwise. More importantly, this type of claim does not challenge any fundamental/predisposed beliefs about the world.

On the other hand, here’s an example of an extraordinary claim: "On the way to the bathroom this morning, Moses appeared and handed me a letter from Elijah."  This statement is actually making quite a few claims that challenge what we already believe about the world: Moses and Elijah (if actual historical figures) are dead; the dead to not return to life (esp. the long-dead); the existence of ghosts is hotly disputed for various reasons, let alone calling into question how an immaterial being can directly interact with the material, physical world.   Moreover, even if the letter is found to be written in a language authentic to the supposed time and place of Elijah’s existence, this does not show that Elijah wrote it.  In short, this claim challenges some fundamental beliefs about life, death, and physics.

Ockham’s Razor[2]
1) If two hypotheses explain the evidence
equally well, choose the simpler.[3]
2) Never add superfluous hypotheses to that
which has been sufficiently explained.[4]

OR basically instructs us to look for prosaic explanations of phenomena.  While it is exciting and fun to spin wild explanations of events (e.g., “Perhaps that light streaking across the sky is an alien visitor.”), OR says to form hypotheses that derive directly from the evidence and never form hypotheses whose evidence is ambiguous or absent (“There is a light streaking through the sky but we need more evidence to conclude aliens.”).  OR’s caution is to try to form an explanation that does not ask more questions than it attempts to answer.

As an example of the first part of OR, with great effort you can force Ptolemy’s geocentric model of the solar system to work and predict the position of the planets.  This is done with “epicycles,” or orbits within orbits (a planet orbits around a point that itself orbits the Earth).  However, this model is clunky and extremely complex because you have to use epicycles within epicycles to make it work.  On the other hand, the heliocentric model also predicts the positions of the planets just as well but does it in an easier, more elegant fashion.[5]  And, as an example of the second part:  While it may be true that gravity and angels both cause planets to revolve around the sun, gravity is enough to explain why they do.

What’s the Harm?
One of the most common challenges skeptics face is “What’s the harm in believing something, even if it’s probably false?”  Well, I guess we could look to the Heaven’s Gate suicides for an answer.  Yes, most of the time believing something causes no one any harm at all, but sometimes it does.  Perhaps if Marshall Applewhite’s followers (and their intellectual cousins) had practiced even a few ounces of skepticism, they wouldn’t have fallen into the trap of dangerous dogma.

Also, it should be noted that even skeptics disagree on some things.  For instance, some skeptics believe in God, although it is not a predominant percentage.  Even Martin Gardner, who I consider to be the skeptic’s skeptic, believes in a supreme being, albeit not the traditional invisible-man-in-the-sky.  However, the good skeptic knows that if he holds a belief that doesn’t hold up to critical inquiry it must be recognized as such by himself and others.  Accordingly, Gardner acknowledges that atheists and agnostics have the better arguments but he believes for emotional reasons.  And who can argue with that?

In addition, I think that some (if not most) people fail to realize that skeptics typically used to be believers themselves.[6]  Even after I rejected my religion as a college freshman, I believed in UFOs and alien abductions, ghosts and specters, Nessie and Bigfoot, even life after death.  Not until I read Carl Sagan’s Demon-Haunted World did I begin to look at these issues in new, critical ways and found that my beliefs in these things were unfounded.

As we have seen, skepticism can be seen as being cynical and negative, if you mean by those terms that skeptics try to find reasons not to accept a belief as being true.  However, the method of skepticism is not only (in my opinion) a favorable world-view, it can be a fascinating journey into the psychology of belief and an uplifting quest for truths.