The defendant in the 1975 case had been convicted of murder and sentenced to life imprisonment. He appealed the conviction on the grounds that the trial judge wrongly refused to admit psychiatric evidence which would have established his provocation defense. Expert evidence was excluded in the case because it dealt with matters of common knowledge and experience. The appeals court decision appeared to be based on an interpretation of the relationship between psychology and common sense. An analysis of legal issues surrounding the admissibility of expert psychological and psychiatric testimony leads the authors to conclude that expert psychological evidence should be admitted whenever it is both relevant and potentially helpful to the jury in explaining aspects of human behavior that are not easily understood with common sense alone. 22 references