The expanded version of the Essaywas a more mature treatise on morals and politics. ‘Population: the second Essay’ deals with the more important themes to emerge from Malthus's revisions of his basic position. The most important change was a reclassification of the checks to population designed to focus on moral restraint as the acceptable alternative to vice within the category of preventive checks operating on birth rates. Hence the moral duty of delaying marriage until there was a prospect of supporting children. It was a duty capable of being understood by all, and it placed responsibility where it belonged, on the person who produces children he cannot support.