Whenever I argue with conspiracy theorists, I often run into a kind of logical fallacy that I’d like to dub the ante hoc fallacy.
In the post hoc, ergo propter hoc (“after this, therefore because of this”) fallacy, the reasoner assumes that because one event follows another, the second was caused by the first.
In the ante hoc (“before this”) fallacy, the non sequitur is reversed: the reasoner assumes that whatever happens after an event is the reason for that event; that is, whatever followed an event was the purpose and intended result of it.
Examples include: “President Bush invaded Iraq after 9/11, therefore 9/11 was done so Bush could invade Iraq.” Or, “President Obama pushed for gun control after Sandy Hook, therefore the Newtown shootings were staged to force gun control.”
My friend Grant suggests fruitur hoc, ergo hunc faciebant (“they benefited by this, therefore they did this”) as a related fallacy, often associated with the misuse of the cui bono? (“who benefits?”) heuristic.