Quote by Sextus Empiricus
The Mode of circular reasoning is the form used when the proof itself which ought to establish the matter of inquiry requires confirmation derived from the matter; in this case, being unable to assume either in order to establish the other, we suspend judgement about both.http://plato.stanford.edu/entries/skepticism/
Summary
Circular reasoning, or circular argumentation, refers to the practice of using a statement to support or prove itself, creating a logical loop. In this quote, the author highlights the mode of circular reasoning as a situation where a proof needed to establish a particular inquiry relies on confirmation derived from that same inquiry. Consequently, the author suggests that in such cases, where there is a lack of ability to assume one in order to establish the other, it is necessary to suspend judgement about both elements until further evidence or reasoning is provided.