Direct oral evidence requires witnesses with first hand perception; expert treatises admissible under specified unavailability conditions. Oral evidence must be direct: testimony must be given by a witness who personally perceived the fact by the relevant sense or manner, and opinions and their grounds must be given by the person holding them. Expert opinions in commonly sold treatises may be proved by producing the treatises if the author is dead, unavailable, incapable, or cannot be called without unreasonable delay or expense. Where oral evidence refers to a material thing (other than a document), the Court may require production of that thing for inspection.