Petitio principii

Petitio principii (begging the question) happens when the conclusion is already assumed in the premises, explicitly or implicitly.

Example

“This outlet is always truthful because it is reliable.”
(“Reliable” is defined by the truthfulness being proved.)

Applied example (political)

“The law is just because it is the law.” (The conclusion is assumed.)

Applied example (mystical)

“Energy works because it is true.” (Hidden circularity.)

Why it is fallacious

• It provides no external evidence.
• The conclusion is restated with other words.
• It blocks verification.

How to spot it

• The proof is equivalent to the conclusion.
• Synonyms hide the circularity.
• No independent data are offered.

How to respond

• Ask for external, verifiable evidence.
• Show the circularity directly.
• Require criteria that do not depend on the conclusion.