The legal concept that opinions of lay witnesses are not admissible evidence is of comparatively recent origin, and a matter of historical accident. The theory underlying the exclusion of opinions of laymen is not one of qualification, but of policy. If the witness testifies as to the facts, his opinion or inference is superfluous, as it is the function of the jury to draw the inferences. The testimony of the agent to the existence of the agency relation is limited by this general rule. It is the purpose of this discussion to determine the line of demarcation between opinion and fact in this situation when the existence of agency is a contested issue. If the agency issue is uncontested, it is adherence to legal formalism to raise the question.
Arthur A. Greene Jr.,
PRINCIPAL AND AGENT - EXTENT TO WHICH AN AGENT MAY TESTIFY AS TO THE EXISTENCE OF THE AGENCY,
Mich. L. Rev.
Available at: https://repository.law.umich.edu/mlr/vol37/iss5/9