Solidarity is unity (as of a group or class) which produces or is based on unities of interests, objectives, standards, and sympathies. It refers to the ties in a society that bind people together as one. The term is generally employed in sociology and the other social sciences as well as in philosophy or in Catholic social teaching.
What forms the basis of solidarity varies between societies. In simple societies it may be mainly based on kinship and shared values. In more complex societies there are various theories as to what contributes to a sense of social solidarity.
Solidarity is also one of six principles of the Charter of Fundamental Rights of the European Union and December 20 of each year is International Human Solidarity Day recognized as an international observance.
According to Émile Durkheim, the types of social solidarity correlate with types of society. Durkheim introduced the terms "mechanical" and "organic solidarity" as part of his theory of the development of societies in The Division of Labour in Society (1893). In a society exhibiting mechanical solidarity, its cohesion and integration comes from the homogeneity of individuals—people feel connected through similar work, educational and religious training, and lifestyle. Mechanical solidarity normally operates in "traditional" and small scale societies. In simpler societies (e.g., tribal), solidarity is usually based on kinship ties of familial networks. Organic solidarity comes from the interdependence that arises from specialization of work and the complementarities between people—a development which occurs in "modern" and "industrial" societies.
Although individuals perform different tasks and often have different values and interest, the order and very solidarity of society depends on their reliance on each other to perform their specified tasks. Organic here is referring to the interdependence of the component parts. Thus social solidarity is maintained in more complex societies through the interdependence of its component parts (e.g., farmers produce the food to feed the factory workers who produce the tractors that allow the farmer to produce the food).