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.

• 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.

• 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.

• 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.

• Circular reasoning – 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 – a statement true by form; only fallacious when posed as proof. Ask: is this presented as an argument (→ petitio), or merely stated (→ tautology)?

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.

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