- Petitio principii (Latin: "pursuit/attack of the source")
"Proving" that something is true by taking your conclusion as one of your premises, usually done implicitly rather than explicitly. Few people are fooled by having your conclusion as your only premise
, as in "Joe is mad at Jill, therefore Joe is mad at Jill.". Such arguments are called tautologies
and are valid, and sound if the premises are true, but utterly meaningless. Put broadly, this fallacy applies to any argument where one or more premises are at least as contentious as the conclusion itself, and for the same reasons, such as:
Alice says she is honest.
If an honest person says something, it must be true.
Therefore Alice is an honest person, because an honest person says so.
"Begging the question" is often used to mean "leading inevitably to the question" (similar to how something can be said to "invite criticism" or someone can be "asking for a smack") in popular media, though this usage is a common Berserk Button
for academics aware of the original use noted above (It doesn't help that the academic meaning is not only horribly counter-intuitivenote
, but also a mistranslation; as stated above, the original Latin means something more like "arguing the source"). Nevertheless, to avoid confusion, this fallacy is sometimes referred to by its Latin name, petitio principii
in more formal settings.
See also No True Scotsman
. If you are arguing with someone and each of you thinks the other is Begging the Question
, then your definitions are different and/or there is mutual Values Dissonance
- A classic Bill Mauldin political cartoon from the early 1960s features an American soldier standing in a field of large cartoon mushrooms, a shout-out to the conical hats worn by Asian field workers and guerrillas, explaining to a comrade the challenge of ground combat in Vietnam: "You got your mushrooms and your toadstools. The mushrooms are harmless, the toadstools will kill you. You'll know it's a toadstool if it kills you."note
- When Van Helsing and company are investigating Lucy's grave in Dracula, Dr. Seward argues "I am satisfied that Lucy's body is not in that coffin, but that only proves... that it is not there."
- Similar to the "mushrooms" example above, in Metal Gear Solid 3, Snake wants to know the difference between two snakes who look very similar, but one of which will poison him if he eats them. Para-Medic suggests an easy way to tell them apart: eat one. If it's poisonous, then he knows it's the poisonous one.
- In the days of Usenet, in a football forum, one poster postulated that you need a great coach to win a Super Bowl. He then defined a "great coach" as one who had won a Super Bowl.
- Watch the TV show Ancient Aliens and marvel at how the proof there were aliens visiting the Earth in the past is how the theory there were aliens that visited the Earth in the past explains problems in history that are problems if you assume there were aliens who visited Earth in the past.
- Descartes' so-called "proof" of the existence of God. Raymond Smullyan demonstrated that the only thing really proved by Descartes is that if there are one or more gods who fit Descartes' definition, then their properties must include existence; not that there necessarily is/are such a god or gods.
- Today, even in Christian circles, it is considered a poor argument that a "proof" of the existence of God is that The Bible says there's a God, and then when pressed on why the Bible should be believed, to answer "Because it's God's word and God doesn't lie." Of course, those statements necessarily require that God exist in order for them to be true.