This article addresses the law's concept of the person and its relation to responsibility and the excusing conditions. It demonstrates that causation of behavior in general, even pathological biological causation, is not itself and excuse and suggests that the incapacity for rationality is the genuline basis of moral and legal excuse. The paper concludes by applying its theses to the case of Spyder Cystkopf, a man with a confirmed subarachnoid cyst, who killed his wife during a heated argument with her.