fallacy

Begging the question

Also called: Circular reasoning, Petitio principii

An argument begs the question when its conclusion is already assumed in its premises, so the reasoning goes in a circle and proves nothing new.

How it works

The conclusion is restated in different words and offered as a premise. Because the wording changes, the circle can be hard to see, and the argument seems to support itself.

Examples

"This newspaper is trustworthy because it says it only publishes the truth."

Trusting the newspaper's claim already assumes it is trustworthy.

"The policy is fair because it treats people justly."

"Treats people justly" is just another way of saying "is fair".

How to spot it

Paraphrase the premise and the conclusion: are they the same claim?
Remove the conclusion: is there any independent reason left?
Definitions are doing the work that evidence should do.

How to respond

Ask for a reason that does not already assume the conclusion.
Point out the restatement plainly and ask for independent support.
Note that "begs the question" in everyday speech often means "raises the question", which is a different thing.