1911 Encyclopædia Britannica/Petitio Principii

PETITIO PRINCIPII, or Begging the Question (Gr. τὸ ἐν ἀρχῇ λαμβάνειν, τὸ ἐξ ἀρχῆς αἰτεῖσθαι), in logic, the fourth of Aristotle’s fallacies ἔξω τῆς λέξεως or extra dictionem. Strictly this fallacy belongs to the language of disputation, when the questioner seeks (petit) to get his adversary to admit the very matter in question. Hence the word principium gives a wrong impression, for the fallacy consists not in seeking for the admission of a principle which will confute the particular proposition—a perfectly legitimate form of refutation—but in luring the adversary into confessing the contradictory. In the ordinary use, however, “begging the question” consists in assuming in the premises the conclusion which it is desired to prove.