- Ultimate Issues – Opinion testimony (lay or expert) generally is permissible even if it addresses an "ultimate issue" in the case (e.g. X was drunk; That's X's signature on the check). BUT, Federal exception: In a criminal case, in which a defendant's mental state constitutes an element of a crime or defense, an expert witness may NOT state an opinion as to whether the accused did or did not have the mental state in issue. (Appears frequently in insanity cases).
Evidence: Testimonial Evidence: Witnesses: Opinion Testimony: Ultimate Issues