Today the courts are almost unanimous in holding that proof of statements made by a witness out of court similar to and in harmony with his testimony are inadmissible. "This rule of evidence," said Mr. Justice Holloway, speaking for the Supreme Court of Montana in the case of Fairleigh v.Kelley (1903), "became settled long ago." It is unquestionably supported by the decided weight of authority, and in fact, it may now be said that the rule is more than general—it is well nigh universal. There are, however, well settled exceptions to this general rule. In fact, the exceptions "have become so well established as now to constitute themselves an independent rule." They are, however, very few in number and rest upon exceptional circumstances. In each case the question is whether the circumstances are such as to make the evidence admissible.
Herald A. O'Neill,
Admissibility of Previous Consistent Statements by a Witness,
Wash. L. & Rev.
Available at: https://digitalcommons.law.uw.edu/wlr/vol6/iss3/2