A “fallacy” is a mode of thought that is asserted (by calling it a “fallacy”) to lead us easily into error, or to not usefully contribute to the project of distinguishing truth from falsehood. For example, Argumentum Ad Hitlerum is a ‘fallacy’ because while Hitler did a number of bad things, he also ate vegetables, so “Hitler did X” is not a reliable means of arguing that nobody should do X.


  • Proving too much

    If your argument could just as naturally be used to prove that Bigfoot exists and that Peano arithmetic is inconsistent, maybe it’s an untrustworthy kind of argument.

  • Bulverism

    Bulverism is when you explain what goes so horribly wrong in people’s minds when they believe X, before you’ve actually explained why X is wrong. Forbidden on Arbital.

  • Emphemeral premises

    When somebody says X, don’t just say, “Oh, not-X because Y” and then forget about Y a day later. Y is now an important load-bearing assumption in your worldview. Write Y down somewhere.

  • Multiple stage fallacy

    You can make an arbitrary proposition sound very improbable by observing how it seemingly requires X, Y, and Z. This didn’t work for Nate Silver forecasting the Trump nomination.

  • Mind projection fallacy

    Uncertainty is in the mind, not in the environment; a blank map does not correspond to a blank territory. In general, the territory may have a different ontology from the map.

  • Invisible background fallacies

    Universal laws also apply to objects and ideas that may fade into the invisible background. Reasoning as if these laws didn’t apply to less obtrusive concepts is a type of fallacy.

  • Gotcha button

    A conversational point which, when pressed, causes the other person to shout “Gotcha!” and leap on what they think is a weakness allowing them to dismiss the conversation.

  • Harmless supernova fallacy

    False dichotomies and continuum fallacies which can be used to argue that anything, including a supernova, must be harmless.