This article is from the alt.usage.english FAQ, by Mark Israel email@example.com with numerous contributions by others.
Fowler defines "begging the question" as the "fallacy of
founding a conclusion on a basis that as much needs to be proved as
the conclusion itself."
"Question" here does not mean "a sentence in interrogative form".
Rather, it means "the point at issue, the thing that the person is
trying to prove". The phrase is elucidated by William Fulke in
"Heskins parleamant repealed" (1579): "O shameless beggar, that
craveth no less than the whole controversy to be given him!" The
OED's first citation for "to beg the question" is from 1581.
Common varieties of begging the question are paraphrase of the
statement to be proved ("Telepathy cannot exist because direct
transfer of thought between individuals is impossible"), and
arguing in a circle ("The Bible must be true, because God wouldn't
lie to us; we know God is trustworthy, because it says so in the
Bible"). Fowler gives two example of non-circular question-begging:
"that fox-hunting is not cruel, since the fox enjoys the fun, and
that one must keep servants, since all respectable people do so".
Gowers notes that single words, such as "reactionary" and
"victimization", can be used in a question-begging way.
The Latin term for the fallacy is "petitio principii", a
translation of the Greek "to en archei aiteisthai"="at the
beginning to assume"; but "aiteisthai" does literally mean "to beg".
The phrase can be traced back to Aristotle (4th century B.C.):
"Begging or assuming the point at issue consists (to take the
expression in its widest sense) in 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 [...]. 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." ("Prior Analytics" II xvi)
Many people unaware of the technical meaning of "to beg the
question" in logic use it in one of two looser senses. The first of
these, "to evade the question, to duck the issue", is attested since
1860 (WDEU). The second, "to invite the obvious question, (with an
inanimate subject) to raise the question", is now the most commonly
heard use of the phrase, although we have found no mention of it
prior to The Oxford Guide to English Usage, 1st edition (1983), and
it is not yet in most dictionaries. The meaning of the adjective
"question-begging" does not seem to have suffered a similar