A brief introduction to conspiracy theory
The field of conspiracy theory is a bit confused because not all the relevant definitions have been standardized. Let us begin with conspiracy, which is a secret agreement to perform an illegal act. Conspiracy is the nominal version of the verb conspire (literally to breathe together), which means to join in a secret agreement to perform an illegal act. The people joining together are the conspirators; the people invoking the conspiracy are the conspiracists. Sometimes the word conspiratorialist is used in place of conspiracist, but it isn't a real word and just confuses things. It should be dropped from the vocabulary. Its root, conspiratorial, means relating to a conspiracy, as in "The planners displayed conspiratorial tendencies." It is sometimes used to refer to people who invoke conspiracies, but this is wrong also.
The big problem is that conspiracy theory is used in two different ways. The first is as a conspiracy theory, which refers to to an explanation that invokes a conspiracy. Although some authors say that the invoked conspiracy is nonexistent, I think it is more appropriate for most cases to say that the conspiracy is unproven. The second use of conspiracy theory is generic, referring to the act of appealing to, or the tendency to appeal to, undocumented conspiracy (or conspiracies) and continuing to appeal to it (or them) for years to centuries without documentation. Unfortunately, this generic use is seldom defined—readers have to figure it out for themselves.
We might also note that the theory in conspiracy theory is used incorrectly. At least in the scientific world, a theory is is an advanced stage of explanation, an idea that was first proposed as a hypothesis, then rose to the level of working hypothesis, and then survived enough tests to ultimately be taken very seriously and regarded as the best explanation. A conspiracy theory usually shares none of these characteristics. By its very nature, it is undocumentable, and hence represents the earliest stage of explanation. It should probably be called a conspiracy hypothesis. But even this term is too strong, because it is an idea that has failed the test of finding concrete evidence for it. Whatever term is appropriate, it is not conspiracy theory.
What conspiracy theories offer their practitioners
Very briefly stated, conspiracy theories offer their practitioners at least these several advantages:
What generates conspiracy theories?
Here there are a great variety of answers.