"Petitio Principii is the name of an argument which assumes the conclusion that is to be proved … “the surreptitious assumption of a truth you are pretending to prove.” Since, then, the fallacy is one of assumption … its source must be found, not in what is definitely asserted, but in the world of reality or existence in which what is asserted has a definite meaning or fulfillment, that is to say, in the universe of discourse from the standpoint of which the argument is interpreted. … Whenever it exists, the fallacy directs attention to the fact that the truth of what an argument asserts depends in part upon what assumptions the argument makes; and, in view of the nature of an argument, it follows that when assumptions are put forward as reasons we necessarily fail to establish a conclusion, and fall into the merest dogmatism unless we are willing to have these assumptions called into question. … Now, when this happens, when in the course of argument assumptions take the place of reasoned judgments, the argument is fallacious because, for the reason assigned, it involves a petitio principii… When the fallacy of petitio principii is committed in a single step it is called … hysteron proteron… and when it involves more than a single step it is called circulus in probando or reasoning in a circle."