Phrenology and the Insanity Defence: Medical Jurisprudence in the McNaughtan Trial

Abstract

This thesis argues that phrenology shaped the defence argument in the McNaughtan trial. The role of this now-discredited science exemplifies the negotiation of scientific, legal and lay knowledge in the early nineteenth century, at a time when science was challenging the primacy of lay understandings of insanity. Phrenological ideas allowed the defence to privilege medical opinion over lay opinion, and propose a model of the mind that could account for McNaughtan’s insanity. This was possible because the medical and professional communities accepted some elements of the science. They applied these principles when explaining and verifying insanity in a courtroom setting.