What is Skepticism?

Our world is awash with people making claims:

"My new homeopathic treatment will cure the flu!" "Dinosaurs roamed the earth millions of years ago." "The world is flat." "God spoke the world into existence 6000 years ago." "The world is round." "I was visited by aliens last night." "Global Warming is a hoax." "Marduk created the earth from the corpse of Tiamat."

Not every claim can be true. But how does one know the difference? You might say common sense. This is true to an extent, but there are a lot of people whose "common sense" tell them a lot of unbelievable things.

To help determine the validity of a claim, you need to employ a process. In the sciences, that process is called the scientific method. Simplified, it goes like this: First, you form a hypothesis ("The world is round."). Then you make observations about your hypothesis (fly a plane around the world, send up a network of satellites). Your observations will either invalidate your hypothesis (your plane smashes into a wall at the edge of the earth), or they won't. If your hypothesis is invalidated, you modify it to fit the new data and repeat until you have a reasonably good model, or "theory," of the way things actually are.

In the strictest sense, no set of observations will ever "prove" a scientific hypothesis. But when there is a huge preponderance of evidence, we can basically accept the hypothesis as true. Very few people today (make no mistake, there are some!) believe that the world is flat because of a preponderance of evidence demonstrating that it is round.

Skepticism takes this same approach and applies it to everything. So, what is skepticism, exactly?

The word "skepticism" has a bit of a bad reputation. You often hear the word "skeptic" in the same sentence as "cynic." All skepticism means is that when people make claims, those claims should be open to testing and should be judged on the quality of the evidence. If the claim being made flies in the face of what we already know, then the burden of proof is on the one making the claim to demonstrate the truth of their claim.

Extraordinary Claims Require Extraordinary Evidence
When you hear a claim, what do you feel is the likelihood of this claim being true, based on what we already know? If someone claims "I lost my keys," you probably won't require a great deal of evidence. People lose their keys all the time. It's not an extraordinary claim.

If, instead, they claim "I can walk through walls," most people will be a lot more skeptical. No one has ever been known to walk through walls before. Furthermore, if someone were able to do so, it would literally require physicist to rewrite their model of the universe from the ground up. It is quite an extraordinary claim. For the most part, claims like this can be dismissed out of hand. That said, a true skeptic will gladly accept such claims as true if the claimant can demonstrate their ability in truly a controlled environment (i.e., not susceptible to trickery or other methods of deception). For instance, the James Randi Educational Foundation, one of the foremost skeptic organizations, has a standing $1,000,000 prize for anyone able to demonstrate a paranormal ability in a controlled environment. To date, no one has claimed the prize.

Religion
Many skeptics consider religion off the table, arguing that people's deeply-held beliefs should not be subjected to scrutiny, and that the claims made by religion are not falsifiable (that is there is no way to test their validity) and are therefore outside the realm of science or skepticism. Other skeptics gladly tackle religious topics, arguing that just because a given claim was written down thousands of years ago, it shouldn't be exempt from skeptical scrutiny. I personally tend to side with the latter group. No claim, particularly any claim upon which people chose to base their entire lives, should be exempt from examination.

Resources
If you'd like to know more about skepticism, I'd like to share a few excellent resources:

• Skeptics' Guide to the Universe - If you only have time for one skeptical resource in your life, make it The Skeptic's Guide to the Universe. This weekly podcast covers the whole gamut of skeptical topics, from alternative medicine to the evolution/creationism debate... And it's seriously entertaining, too.
• The Demon-Haunted World - Carl Sagan's book is a superb primer to the world of skepticism and rationality in a world plagued with claims of the supernatural and paranormal. It's a quick read, very accessible and tremendously enlightening.
• Skeptic Magazine - Run by Michael Shermer, who along with James Randi is one of the best known faces of skepticism in the public eye, Skeptic Magazine is a great addition to any Skeptical Tool Kit.
• Skepchick - Run by Rebecca Watson, one of the host of the Skeptics' Guide, the Skepchick blog features a plethora of skeptical women (and one dude) who don't hold back any punches. Add Skepchick to your RSS reader! Now!
  

There are hundreds of other skeptical blogs, podcasts and other media available. But that should get you started. Have fun!