A conspiracy theory is an explanation of an event or situation that invokes a conspiracy without warrant, generally one involving an illegal or harmful act carried out by government or other powerful actors. Conspiracy theories often produce hypotheses that contradict the prevailing understanding of history or simple facts. The term is a derogatory one.[3] According to the political scientist Michael Barkun, conspiracy theories rely on the view that the universe is governed by design, and embody three principles: nothing happens by accident, nothing is as it seems, and everything is connected.[1]:3–4 Another common feature is that conspiracy theories evolve to incorporate whatever evidence exists against them, so that they become, as Barkun writes, a closed system that is unfalsifiable, and therefore "a matter of faith rather than proof".