Durkheim's theory is phrased in terms of the historical development of society from a primitive to an advanced stage. Law and punishment take very different forms in this societal evolution, and punishment is one of the most fundamental means by which social solidarity is maintained. The punishment of criminals bonds law-abiding members of society into a coherent group. Therefore, punishment serves socially useful functions, independent of its effect on criminal behavior. Durkheim's theory projects a society in which criminal law, with its emphasis on retributive punishment, simply fades from the scene. What remains is essential civil law in which individuals file grievances against each other. Marx's theory is basically an economic interpretation of history rather than a theory of individual or group behavior. Criminal punishment serves two purposes in capitalist societies, according to Marx. First, punishment responds to the proletariat's criminal behavior. Second, punishment is used by the ruling class as one of many tools to maintain control. He believes that the evolutionary development of capitalist societies is in the direction of increased crisis. Simmel focuses on understanding and describing current societies. He holds that society consists of all reciprocal relationships between individuals. The extent to which a group is tightly knit can be gauged by the extent to which it has a code of honor regulating member behavior. His theory implies that negative consequences of conflict, such as crime and punishment, can be reduced if isolated individuals are bonded to a group representing their values and interests.