The distinguishing characteristic of evidence also can be, and has been, a matter for dispute; some have denied that evidence is a guarantee of truth. To be sure, the people who make this claim are usually so inconsistent that they do not want to be sceptics. For they wish, at the same time, to know how to distinguish true judgments from false, and if we ask them what constitutes the distinction, they reply that it is universal correspondence in judging. Where this correspondence is present, the judgment is to be termed true, where it is absent, false. If we inquire further how we are to recognize this correspondence, they do not know what to say, or else they become ensnared in a vicious circle. In any case, general correspondence, even where it exists and its existence can be established, can be no substitute for insight. Thus more consistency was displayed by the ancient sceptics, with their doctrine of the arbitrariness of our principles. But even they were not consistent; no sceptic can possibly be. For if there is no such thing as insight, we can also have no insight into the impossibility of knowledge. We would not even be justified in asserting that our principles are arbitrary; indeed, every claim would be a defection from the basic thesis. Hence it was that Aristotle said silence was the only suitable stance for a sceptic-and silence deprives him of the possibility of teaching scepticism.