Conventional sociological theory is unable to account for endogenous change at the structural level. While various sociologists have attempted to develop a framework that would account for such change by abstracting formalized elements out of Marxist theory, these efforts--precisely because of their highly formal nature--are unsuccessful. Marx's theory itself seeks to explain change as built into the contradictory survival requirements of class societies conceived as closed social systems. The forces militating for change play themselves out with quasi-automatic necessity. The direction of change depends partly on the structural parameters and partly on the consciousness of individuals organized into social classes. It is argued that the utility of Marx's approach is tied both to his overall theoretical framework, and its rootedness in specific historical, social and economic conditions. This argument is illustrated with reference to Marx's theory of the falling rate of profit under conditions of competitive capitalism.