The original phrase used by Aristotle from which begging the question descends is: τὸ ἐξ ἀρχῆς (or sometimes ἐν ἀρχῇ) αἰτεῖν, "asking for the initial thing." Aristotle's intended meaning is closely tied to the type of dialectical argument he discusses in his Topics, book VIII: a formalized debate in which the defending party asserts a thesis that the attacking party must attempt to refute by asking yes-or-no questions and deducing some inconsistency between the responses and the original thesis.
In this stylized form of debate, the proposition that the answerer undertakes to defend is called "the initial thing" (τὸ ἐξ ἀρχῆς, τὸ ἐν ἀρχῇ) and one of the rules of the debate is that the questioner cannot simply ask for it (that would be trivial and uninteresting). Aristotle discusses this in Sophistical Refutations and in Prior Analytics book II, (64b, 34–65a 9, for circular reasoning see 57b, 18–59b, 1).
The stylized dialectical exchanges Aristotle discusses in the Topics included rules for scoring the debate, and one important issue was precisely the matter of asking for the initial thing—which included not just making the actual thesis adopted by the answerer into a question, but also making a question out of a sentence that was too close to that thesis (for example, PA II 16).
The term was translated into English from Latin in the 16th century. The Latin version, petitio principii, "asking for the starting point", can be interpreted in different ways. Petitio (from peto), in the post-classical context in which the phrase arose, means assuming or postulating, but in the older classical sense means petition, request or beseeching.[1][4] Principii, genitive of principium, means beginning, basis or premise (of an argument). Literally petitio principii means "assuming the premise" or "assuming the original point".
The Latin phrase comes from the Greek τὸ ἐν ἀρχῇ αἰτεῖσθαι (to en archei aiteisthai, "asking the original point")[5] in Aristotle's Prior Analytics II xvi 64b28–65a26:
Begging or assuming the point at issue consists (to take the expression in its widest sense) [of] failing to demonstrate the required proposition. But there are several other ways in which this may happen; for example, if the argument has not taken syllogistic form at all, he may argue from premises which are less known or equally unknown, or he may establish the antecedent by means of its consequents; for demonstration proceeds from what is more certain and is prior. Now begging the question is none of these. […] If, however, the relation of B to C is such that they are identical, or that they are clearly convertible, or that one applies to the other, then he is begging the point at issue…. [B]egging the question is proving what is not self-evident by means of itself…either because predicates which are identical belong to the same subject, or because the same predicate belongs to subjects which are identical.
— Aristotle, Hugh Tredennick (trans.) Prior Analytics