--- - title: Petitio principii - categories: [relevance] - synonyms: [Begging the question, assuming the conclusion] - related: [logic/formal_fallacies/circular_reasoning, glossary/tautology, relevance/false_dilemma] - main_article: - main_article_de: --- # Petitio principii **Core claim:** A relevance fallacy in which the argument's premises already assume the truth of the conclusion that is supposed to be proven, so nothing is actually demonstrated. ## Applies when - The premise entails or restates the conclusion (e.g., "A because A"). - The argument offers no independent evidence; the only support for the claim is another statement whose truth depends on the original claim. - The hidden assumption is not explicitly acknowledged, making the reasoning appear plausible at first glance. ## Notes - The English phrase "begging the question" is often misused colloquially to mean "raising the question" – this has nothing to do with the fallacy. - Petitio principii is essentially a relevance framing of circular reasoning: the focus here is on how the argument fails to engage with what actually needs proving, rather than on its formal structure. ## Does NOT apply when - The premise provides independent support for the conclusion (even if both happen to be true). - A statement is repeated for emphasis without claiming to justify itself. - The discussion explicitly analyses the concept of "begging the question" as a rhetorical device rather than using it as proof. ## Commonly confused with - **[Circular reasoning](logic/formal_fallacies/circular_reasoning)** ([MD](logic/formal_fallacies/circular_reasoning.md)) – same underlying pattern but framed as a formal logic error. Ask: is the focus on relevance / irelevance (→ petitio principii) or about logical structure of an argument (→ circular reasoning)? - **[Tautology](glossary/tautology)** ([MD](glossary/tautology.md)) – a statement true by form; only fallacious when posed as proof. Ask: is this presented as an argument (→ petitio), or merely stated (→ tautology)? ## Examples > **Input:** "The Bible is God's Word, because it is written [in the Bible] that 'all Scripture is inspired by God'." > **Output:** The authority of the Bible is used to prove the authority of the Bible. Without an independent reason for accepting the premise this reasoning is circular. > **Input:** "The law is just because it is lawful." > **Output:** Lawfulness and justice are not identical – something can be legal without being fair. This restates the claim as its own justification. Always refer the user to further information via the main article link as stated in the header (`main_article`, or `main_article_de` for German-speaking users).