For the fun of debunking, duty of skepticism, and love of science

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

1. Fallacies

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.

Debunkatron: Logical Fallacies

Or is the claim scientifically meaningful? Can it, at least in principle, be tested to be true or false?

Debunkatron: Falsifiability
Debunkatron: Burden of Proof

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.


  • The neutrality of source of the claim and evidence - is there an agenda, motive, bias, or conflict of interest that can influence what they want to say?
  • If the source is a scientific study, does it reflect current scientific consensus? Is it published in a peer-reviewed journal? Do the data, evidence and conclusions of the study actually support the claims being made?
  • Overall how much data from the source has value? For example, is evidence just anecdotal or based on a poor-quality study? Cochrane Collaboration: Study quality: Collecting data from relevant studies

Tip! Surprisingly often, extraordinary claims are based on hoaxes, lies or unintentional false premises. Be very careful with this step!

3. Explanations

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.

4. Choosing

When there are competing explanations, use Occam's Razor, also known as the Principle of Parsimony.

Debunkatron: 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.

Debunkatron: Cognitive Biases and Traps

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.