The sociologist Emile Durkheim theorized that there are two types of social solidarity: mechanical, in which people are united through their uniformity of purpose and activity, and organic, in which unity is formed through social interdependence. The term anomie is derived from a Greek word meaning "without law". Anomie comes into play when society, and the individuals within it, are in a state of transition from mechanical to organic solidarity, generally in response to a large scale social change like urbanization. During this transition, people find themselves lacking social laws to follow. They no longer know to what group or entity they should look to for their social norms. This displacement causes anomie.