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Bulverism is a logical fallacy in which one party simply assumes that the other party is wrong and explains their reasons for wanting to believe it rather than addressing the argument itself. It combines Begging the Question with the Genetic Fallacy.

The Other Wiki expresses Bulverism as:

In short, it can be summarized as "You're only claiming X to be the case because you want X to be the case!". This is fallacious since whether or not someone wants something to be true because it would benefit them personally has no bearing on whether or not it actually is.

The term was coined by C. S. Lewis in an essay of the same name in which he describes the (fictional) origin of the fallacy: a boy named Ezekiel Bulver heard his parents arguing when his mother said "Oh you say that because you are a man." at which point Bulver realized that "refutation is no necessary part of argument".

Lewis himself summed up the fallacy as "to assume without discussion that he [your opponent] is wrong and then distract his attention from this (the only real issue) by busily explaining how he became so silly."

Similar to Fallacy Fallacy, Ad Hominem, and Argumentum Ad Lapidem in that the opponent is finding or inventing biases in the other's argument rather than addressing the argument itself. Also related to Hitler Ate Sugar, where a viewpoint is fallaciously discounted because somebody who held it was a bad actor.


  • Both atheists (such as George Rey) and theists (such as Paul Vick) frequently assume that the other side is wrong, then attempt to explain how they fell into error. To elaborate on the given examples, Rey claims theists are self-deceived. Vick argues atheists lacked a strong father growing up, and therefore cannot believe in a fatherly God.
  • Communists in the past have alleged that those who don't believe in communism do so because of "false consciousness" (if they're working-class) or, if bourgeois, won't because it goes against their class interest.
  • Those with extremist political and social views often employ this tactic. If another does not agree with them, they are clearly "afraid to say what everyone thinks", white knighting or trolling in a bid for attention, or perhaps internalizing these opinions when the person is white, black, female, etc. themselves.
  • A very common argument against legalizing drugs is to assume that those on the pro-legalization side are themselves drug addicts or pushers. In fact, it wasn’t until a plurality of the public started to support decriminalizing marijuana that this stopped being the knee-jerk first response, though it’s still used on occasion.

Looks like this fallacy, but is not:

  • Satire is a literary genre whose whole purpose is to subject one’s opponents to ridicule, so it’s generally accepted for purposes of hyperbole. For example, Doctor Strangelove implies that American Cold Warriors are only Cold Warriors because they suffer erectile dysfunction, but this is done to demonstrate the insanity of Mutually Assured Destruction.
  • When one actually has refuted the opponent, then it’s not fallacious to speculate on why they believe nonsense, though it’s still very rude. So it wouldn’t be this fallacy to dismiss a circle-squarer as only holding their belief because they are a crank or mentally ill, since squaring the circle with a compass and straightedge has been proven impossible (since this would require pi to be algebraic when it is in fact transcendental). The problem comes when one already assumes that one is obviously right and one’s opponent obviously wrong to the point that one assumes the opponent came to their position in bad faith, before the debate even begins.
  • Sometimes people will play the Devil’s advocate, arguing for a position that they don’t hold, in order to test whether it has been unfairly maligned (or, potentially, unduly credited). This is a valid technique known as “steelmanning” and is not fallacious, but sometimes a person arguing that a position is not as bad as traditionally believed, or not as good as such, is mistaken for using this fallacy. This is only really true if the defenses are ad hoc reasoning.