A rescript of Hadrian says that “it is impossible to define strictly the amount and mode of proof needed on each issue. The truth can often but not always be found without recourse to public records. Sometimes the number of witnesses, sometimes their dignity and authority, at others common knowledge settles the truth of the matter in issue. In short, all I can reply to you is that a judicial inquiry should not be tied at once to a single mode of proof. You must judge from your own conviction what you believe and what you find not proved.”
