Begging the Question

Fallacy
Let $p$ be a proposition whose truth value is to be proved (either true or false).

Suppose a logical argument is created which uses $p$ as a premise.

That is, that the proposition to be derived is used to derive itself.

Then the fallacy of begging the question has been perpetrated.

Also see

 * Denying the Antecedent
 * Affirming the Consequent