1. Occam's Razor
When it comes to assumptions, that which is simple is more likely to be true, while that which is complicated is less likely to be true. This thought tool, in essence, is Occam's Razor.
Over the years, Occam's Razor has scythed down a great many scientific ideas, treasured beliefs, and imaginative ideas. Uscinski and Parent believe it's also useful for ascertaining truth in conspiracy theories.
"This suggests that we search among competing conspiracy theories for... the one that explains the most of the outcome with the fewest explanatory factors. An alleged scheme may become so complicated that even the most nimble conspirators could not pull it off."
They use the conspiracy theory that 9/11 was an inside job as an example.
"The key contention is that carefully set charges, rather than the airplanes, took down World Trade Center buildings 1, 2, and 7. This would require several things to be true. Dozens of actors would have to set charges in a number of busy buildings without detection. The charges would have to be set in such as way as to blow up the buildings in the exact locations that the planes crashed, which implies ace pilots. And the fuel-laden planes could not impair the charges or else the charges could not detonate more than an hour after impact. Following the feat, Bush Cheney, the 9/11 Commission, FBI, CIA, NYPD, major news outlets, and Popular Mechanics magazine would all have to collude to conceal explosives, destroy evidence, and deceive the public. Comparing this story to the official version, one could see how it is fairly complicated and might be rejected on these grounds."
But Occam's Razor alone isn't necessarily powerful enough to cut down a conspiracy theory. Let's move on to the next test.