We recount how Jean-Étienne Dominique Esquirol (1772–1840) gradually changed his position towards what Philipe Pinel (1745–1826) referred to as mania without delusion. Between 1805 and 1838, Esquirol moved from outright rejection, questioning the very idea of insane persons committing motiveless acts of violence without delusion, to relative acceptance. He eventually incorporated the clinical characteristics of mania without delusion in his description of homicidal monomania, dividing them between reasoning monomania and instinctive monomania. We examine this change by detailing each of Esquirol’s points of disagreement, which decreased sharply between the completion of his thesis in 1805 and the publication of his chapter on homicidal monomania in 1838.