Nor was the conundrum of wants and needs difficult when the world seemed divided between poor people with needs and wealthy people with luxuries. But the complexities of the late nineteenth century increasingly called for answers too specific for the labor theory of value. A solution came through the method of marginal analysis. The concept is easily expressed through calculus, but there was more to the adoption of marginalism than the availability of mathematical technique. Before marginalism, economic activity tended to be conceptualized in fixed terms, moving around blocks of categories into different positions.
Historians are probably already familiar with related concepts as they apply to modernism.
To Marshall, however, the Principle of Continuity involved more than the vision of economics as a process. The objects of study in economics were themselves linked by continuity. The more simple and absolute an economic doctrine is, the greater will be the confusion which it brings into attempts to apply economic doctrines to practice, if the dividing lines to which it refers cannot be found in real life. There is not in real life a clear line of division between things that are and are not Capital, or that are and are not Necessaries, or again between labour that is and is not Productive. This could be read as an attack on the concept of classes, but Marshall accepted the reality of classes as did most of his cohorts.