Both law and medicine are interpretive practices, and both systems have historically worked in tandem, however ineffectively or tumultuously. The law is, by social mandate, imagined as a "fixed" system of social control, made up of rules and procedures grounded in a reality that is independent of language; although we know that law is both revised and interpreted every day in courtroom practice, to imagine the law, the system that keeps bad people behind bars and good people safe, as indeterminate or, worse, fallible, produces social anxieties that upend our cultural assumptions about fairness that predate our judicial system. This imaginary stability, then, is ultimately what prevents the legal system from evolving in consonance with developments in the mental health professions, as inadequate as that discursive system may be for describing and categorizing the infinite possibilities of mental illness, specifically where it is relevant to the commission of a crime. Ultimately, the insanity plea raises the specter of the endless interpretability of the law and mental illness and, therefore, the frailty of the justice system, which makes each insanity defense trial emblematic of larger social anxieties about social control, fairness, and susceptibility to mental illness or the actions of mentally ill people.