petitio principii

Definition

The logical fallacy of begging the question (i.e., "assuming the conclusion").

Etymology

From Latin petītiō prīncipiī (literally “an assumption from the beginning”), calque of Ancient Greek τὸ ἐν ἀρχῇ αἰτεῖσθαι (tò en arkhēî aiteîsthai, “to assume from the beginning”).

Example Sentences

• "A somewhat similar objection has been made by Locke and others, to the effect that the ordinary demonstrative syllogism is a petitio principii."
• "The Streitberg-Michels Theory is evidently a petitio principii. To explain ē in gēbum, it is from the outset taken for granted, for inadequate reasons of method, that the form must be a perfect. [italics original]"