How does the claim that diamonds are valuable because they are expensive beg the question?

The claim that "diamonds are valuable because they are expensive" is a circular argument, a logical fallacy known as petitio principii or "begging the question."

This statement is considered an immediate argument because it assumes the truth of the conclusion within the premise. By asserting that diamonds have value based on their high price, the argument equates "value" with "expense" without providing any independent reasoning or evidence to support why they are valuable in the first place. Because the premise and the conclusion are essentially identical—stating that something is valuable because it costs a lot—the argument fails to prove its point; it merely restates the same information in a circular fashion.1