Quick Manual of Skeptical Tools
Find the best possible knowledge regarding what is true with a claim, in light of the current best available evidence
If the subject of suspicion is a claim, check if the claim is logically valid; in other words, check that the claim is not based on one or more logical fallacies.
Or is the claim scientifically meaningful? Can it, at least in principle, be tested to be true or false?
Tip! It is not important to remember fancy Latin names of fallacies, but make sure you understand why each fallacy is logically incorrect.
2. Premises & Evidence
Before starting to think through the cause, explanation or answer for strange phenomenon or claims, first try to find evidence if such phenomenon even ever happened or if such claim has any connection to reality.
Tip! Surprisingly often, extraordinary claims are based on hoaxes, lies, or unintentional false premises. Be very careful with this step!
Can the phenomenon be better explained?
(Some of these explanations overlap.)
Tip! Many of the listed effects or phenomena can occur in many forms. For example, pareidolia can also be auditory, and placebo effect has many different underlying causes.
When there are competing explanations, use Occam's Razor, also known as the Principle of Parsimony.
In other words, what explanation most fully explains the phenomenon while introducing the fewest (especially unwarranted) assumptions? Example: one pink invisible unicorn used as an explanation introduces many new assumptions such as existence of unicorns, existence of invisible animals which further requires new physics, etc.
Tip! The more ridiculous or extraordinary the claim is, the stronger the evidence to support it should be! Sometimes the best answer is "I don't know" or "I don't know but the evidence doesn't support that claim."
5. Be ready to change your mind!
Science will progress, better studies will be done, contradicting evidence may be found, etc. Nothing should be considered as the final unchanging Truth; however the more validated a theory is, the more likely it is correct, and less likely the results of a single study should be used to discard it.
Be aware of your own biases when evaluating the evidence. Bias can prevent you from recognizing and accepting valid evidence.
Tip! Maybe you were wrong from the beginning!
Be Respectful! The Goal is to assess the claim, not to berate the claimant.
Thanks to Jussi Lahtinen, John Ellis, Erik Harris, Ed Stockly, Mike Bohler, and Ryan Lewis of the Skeptalk Email Discussion List.