Michel Foucault famously opens Discipline and Punish by comparing the horrific eighteenth-century execution of Robert-Francois Damiens to a meticulous nineteenth-century prison timetable. The purpose of prisons was to habituate prisoners to routines and modes of comportment, such that they would engage in these practices without thinking or questioning and would eventually find them comforting and necessary. Foucault makes clear that the prison fails spectacularly at rehabilitating prisoners, and the prison is "dangerous when it is not useless". Foucault observes in Discipline and Punish that penal reformers in the late eighteenth and early nineteenth centuries suggested a variety of approaches to punishment other than prison. Private prisons are paid per prisoner and thus have an interest in seeing incarceration rates rise, prison sentences extended and probations denied. Foucault's argument about the political instrumentality of prisons has been central to the critical prison studies scholarship that has emerged in the 40 years since Discipline and Punish was published.