How does a circular argument assume the conclusion that it is supposed to prove?

A circular argument, or petitio principii, assumes the conclusion it intends to prove by incorporating that conclusion into its premise, either explicitly or implicitly. Instead of offering independent evidence or reasoning to support a claim, the argument relies on the assumption that the claim is already true.1

Because the premise and conclusion are essentially identical, the argument fails to provide genuine support for its position. If the two components were swapped, the statement would appear to remain "proven," demonstrating that no actual logical progression has occurred.1

This fallacy manifests in several ways:
* Immediate arguments: Stating that a conclusion is true simply because a premise restates it (e.g., "Diamonds are worth a lot because they are expensive").1
* Circular reasoning: Using a chain of two or more arguments that eventually loop back to the initial, unproven assumption.1
* Repetition: Simply restating the premise as the conclusion (e.g., "It’s bad because it’s bad").1

Ultimately, while a circular argument might contain true statements, it is considered a logical fallacy because it lacks the good reasoning necessary to establish a conclusion.1