After 1848, Marx's work begins to be influenced by political economy's treatment of machines and by the related energeticist concepts of the nascent science of thermodynamics. These influences shape and trans- form some of Marx's basic premises about the interaction between human beings and the natural world. This transformation changes the meaning of two basic concepts of Marx's later political philosophy: the concept of labor, or work, and the concept of revolution. In this later political philosophy, Marx's key concepts are themselves undergoing a revision of sense.