Circular reasoning

Circular reasoning (Latin: circulus in probando) is a logical fallacy in which the reasoner begins with what they are trying to end with.

Quotes

 * How is it possible to determine what justly may be called science and truth, if the determination itself presupposes the methods of achieving scientific truth? The same vicious circle is involved in any justification of scientific method by the observation of science. … Doubtless the logical fallacy at the very root of the positivist attitude merely betrays its worship of institutionalized science. … If science is to be the authority that stands firm against obscurantism, … philosophy must formulate the concept of science in a way that expresses human resistance to the threatening relapse into mythology and madness, rather than further such a relapse by formalizing science and conforming it to the requirements of the existing practice.
 * Max Horkheimer, Eclipse of Reason (1947), p. 76-77