The hearsay rule is a nonconstitutional rule of evidence which obtains in one form or another in every jurisdiction in the country. The rule provides that in the absence of explicit exceptions to the contrary, hearsay evidence of a matter in dispute is inadmissible as proof of the matter. Although jurisdictions define "hearsay" in different ways, the various definitions reflect a common principle: evidence that derives its relevance in a case from the belief of a person who is not present in court—and thus not under oath and not subject to cross-examination regarding his credibility—is of questionable probative value.
The Constitution does not explicitly refer to the hearsay rule or implicitly constitutionalize the hearsay rule in civil or criminal cases generally; but it does contain two provisions that share common purposes with the hearsay rule. The treason clause of Article III, section 3, prohibits a conviction for treason "unless on the testimony of two witnesses to the same overt act, or on a confession in open court." In cramer v. united states (1945) the Supreme Court construed this clause to require the federal government to produce witnesses who possessed direct evidence—as opposed to circumstantial evidence—of the same overt act. Although Cramer itself did not involve hearsay evidence, its reasoning applies as well to hearsay evidence of overt acts, because hearsay evidence is itself a kind of circumstantial evidence.
The other provision of the Constitution that bears on the hearsay rule is the Sixth Amendment's confrontation clause, which entitles the accused in a criminal case "to be confronted with the witnesses against him." In contrast to the hearsay rule, the confrontation clause does not treat hearsay evidence as presumptively inadmissible against the accused, and it does not treat traditional exceptions to the hearsay rule as automatically admissible. Nevertheless, the confrontation clause addresses the questionable nature of hearsay evidence by requiring the state to produce at trial the hearsay declarants whose statements it uses against the accused, when it appears that the declarants are available to testify in person and that the defendant could reasonably be expected to wish to examine them in person at the time their hearsay statements are introduced into evidence.
(see also: Compulsory Process, Right to.)
Mc Cormick, Charles 1972 Evidence, 2nd ed. Pages 579–756. St. Paul, Minn.: West Publishing Co.