From Scientific American:
...[W]e cannot just dismiss all such theories out of hand, because real conspiracies do sometimes happen. Instead we should look for signs that indicate a conspiracy theory is likely to be untrue. The more that it manifests the following characteristics, the less probable that the theory is grounded in reality:
- Proof of the conspiracy supposedly emerges from a pattern of “connecting the dots” between events that need not be causally connected. When no evidence supports these connections except the allegation of the conspiracy or when the evidence fits equally well to other causal connections—or to randomness—the conspiracy theory is likely to be false.
- The agents behind the pattern of the conspiracy would need nearly superhuman power to pull it off. People are usually not nearly so powerful as we think they are.
- The conspiracy is complex, and its successful completion demands a large number of elements.
- Similarly, the conspiracy involves large numbers of people who would all need to keep silent about their secrets. The more people involved, the less realistic it becomes.
- The conspiracy encompasses a grand ambition for control over a nation, economy or political system. If it suggests world domination, the theory is even less likely to be true.
- The conspiracy theory ratchets up from small events that might be true to much larger, much less probable events.
- The conspiracy theory assigns portentous, sinister meanings to what are most likely innocuous, insignificant events.
- The theory tends to commingle facts and speculations without distinguishing between the two and without assigning degrees of probability or of factuality.
- The theorist is indiscriminately suspicious of all government agencies or private groups, which suggests an inability to nuance differences between true and false conspiracies.
- The conspiracy theorist refuses to consider alternative explanations, rejecting all disconfirming evidence and blatantly seeking only confirmatory evidence to support what he or she has a priori determined to be the truth.