Substantive evidence persuades the trier of fact on issues, distinct from impeachment evidence that discredits witnesses. Substantive evidence is evidence offered to prove a fact in issue and to persuade the trier of fact on propositions determining the tribunal's decision, contrasted with impeachment evidence which is designed to discredit a witness and diminish the effectiveness of his testimony; character evidence or prior acts may, when offered to prove guilt or innocence, operate as substantive evidence rather than merely as impeachment.