Moral and legal responsibility is diminished in neuropsychiatric patients who lack the capacity to use reasoning to determine morally appropriate behavior. Patients with behavioral-variant frontotemporal dementia (bvFTD), however, develop immoral behaviors as a result of their disease despite the ability to explicitly state that their behavior is wrong. In order to determine whether bvFTD patients should be held responsible for their immoral behavior, we begin by discussing the philosophical concepts of free will, determinism, and responsibility. Those who believe in both determinism and free will are called compatibilists. We argue that reason-responsiveness, a specific type of compatibilism, cannot fully determine responsibility in bvFTD patients if reason-responsiveness is considered to be a single, unified concept. Instead, we argue that several different neuropsychological capacities, including many that are impaired in bvFTD patients, contribute to a patient’s ability to respond to certain reasons in specific situations. Finally, we propose a new framework for understanding reason-responsiveness, using case examples to illustrate how this model can be used to determine responsibility in neuropsychiatric patients.