Hill v. Louisville & Nashville Railroad

In the law of evidence no principle is more familiar than that which ordinarily excludes the opinion of a nonexpert witness. One who is called to testify is generally restricted to proof of facts within his personal knowledge, and is not permitted to express his opinion concerning matters which the jury are required to decide. Omne sacramentum debet esse de certa scientia. McKelvey says, “Upon the question of the. existence or nonexistence of any fact in issue, whether a main fact or evidentiary fact, the opinion of a witness as to its existence or nonexistence is inadmissible.” Evidence,…