The way in which mental incapacity in criminal law has been approached to date has not produced a thorough understanding of it. The idea that mental incapacity's chief relevance in criminal law is as a basis for exculpation dominates the scholarship—both doctrinal and philosophical—on mental incapacity. In an effort to advance scholarly understanding of this area of criminal law, this article provides a reconstruction of the legal terrain concerned with mental incapacity—organized as mental incapacity doctrines, a subset of which is exculpatory. In my reconstruction, what unites the relevant aspects of the law is that each doctrine imagines an abnormal subject of the law, and where the doctrines are exculpatory, the evaluative inquiry is not indexed to the reasonable person. This reconstruction of mental incapacity in criminal law—as mental incapacity doctrines—cuts across existing categorizations of this terrain and, as such, offers a rethinking of this area of the criminal law. This reconstruction permits a reconceptualization of the role of mental incapacity in criminal law: it becomes clear that mental incapacity is the basis for doctrines which perform a multiplicity of roles—inculpation, imputation, and a procedural role—beyond exculpation.