Begging the question
Also called: Circular reasoning
Using the conclusion as one of the reasons for the conclusion.
How to spot it
Does the argument only work if you already accept what it is trying to prove?
Example
“The book is true because it says so, and it wouldn't lie.”
How to answer it
Ask for a reason that doesn't assume the conclusion.
Related
- No true Scotsman: Protecting a claim by redefining the group so counterexamples don't count.
- Loaded question: Asking a question that has a disputed assumption built into it.