Argumentum ad lapidem

Argumentum ad lapidem (Latin: "to the stone") is a logical fallacy that consists in dismissing a statement as absurd without giving proof of its absurdity. The form of argument employed by such dismissals is the argumentum ad lapidem, or appeal to the stone.

Ad lapidem statements are fallacious because they fail to address the merits of the claim in dispute. Ad hominem arguments, which dispute the merits of a claim's advocate rather than the merits of the claim itself, are fallacious for the same reason. The same applies to proof by assertion, where an unproved or disproved claim is asserted as true on no ground other than that of its truth having been asserted.

The name of this fallacy is attributed to Dr. Samuel Johnson, who refuted Bishop Berkeley's immaterialist philosophy (that there are no material objects, only minds and ideas in those minds), by kicking a large stone and asserting, "I refute it thus." This action, which fails to prove the existence of the stone outside the ideas formed by perception, fails to contradict Berkeley's argument, and has been seen as merely dismissing it.

Example

• Speaker A: Infectious diseases are caused by microbes.
• Speaker B: What a ridiculous idea!
• Speaker A: How so?
• Speaker B: It's obviously ridiculous.

Speaker B gives no evidence or reasoning, and when pressed, claims that Speaker A's statement is inherently absurd, thus applying the fallacy.

See also

• Proof by assertion
• Ad hominem
• Solvitur ambulando