Divisions within a society based on economic position, occupation, education and status. How class should be defined has been argued about for as long as it has been studied, and the competing definitions measure genuinely different things.
Karl Marx defined class by relationship to the means of production. Those who own productive property and those who sell their labour occupy structurally opposed positions, and the conflict between them drives historical change. Class on this account is a relationship, not a ranking.
Max Weber argued that this was too narrow and identified three dimensions. Class, meaning economic position in markets. Status, meaning social honour and lifestyle, which need not follow wealth. And party, meaning organised political power. An impoverished aristocrat and a wealthy merchant illustrate why the dimensions must be separated.
Pierre Bourdieu extended the idea to forms of capital beyond the economic. Cultural capital comprises education, taste and familiarity with legitimated culture; social capital comprises networks and connections. His argument was that these are transmitted within families and convert into economic advantage, which explains how position reproduces itself without formal inheritance of property.
Occupational schemes, used in most official statistics, classify by employment relations and conditions, distinguishing employers, the self-employed, and employees by security, autonomy and prospects.
Many historical societies had legally defined orders with different rights, which makes them easier to describe than modern stratification.
Estates in medieval Europe divided clergy, nobility and commoners, with distinct legal privileges and obligations.
Caste in South Asia is hereditary, associated with occupation, and enforced through rules about marriage and contact. It is not simply a class system, since it operates through ritual purity as well as economics, and discrimination on its basis is constitutionally prohibited in India while persisting in practice.
Slavery is a legal condition rather than a class position, and its existence means a society is stratified by ownership of persons as well as by ownership of property. Its abolition did not remove the stratification it produced, and the relationship between historical enslavement and present inequality is extensively documented in several countries.
Contemporary research generally measures several things at once, because they diverge.
Income, meaning the flow of earnings, is the easiest to measure and the least stable.
Wealth, meaning accumulated assets, is far more unequally distributed than income in every country where both are measured, and it is more strongly associated with long-term outcomes.
Occupation captures conditions, security and autonomy that income does not.
Education is both a determinant of position and a marker of it.
Subjective class identification, meaning what people say they are, correlates only loosely with any objective measure, and in several countries large majorities identify as middle class regardless of position.
Social mobility measures how far position is inherited, and it is the aspect with the clearest empirical findings.
Intergenerational mobility varies substantially between countries. Nordic countries show weaker association between parental and child income than the United States and the United Kingdom, and the difference is large enough to have entered political argument in all of them.
Mobility is lower than most people believe. Surveys consistently find that populations overestimate how much movement occurs, particularly in countries where mobility is comparatively low.
Multigenerational studies using surnames have found that advantage persists over far longer spans than parent-to-child studies suggest, indicating that families rather than individuals are the persisting unit.
Education is the main proposed mechanism for mobility and functions in both directions, since access to education is itself unequally distributed.
Some argue that class has weakened as an explanation, pointing to declining class-based voting, the fragmentation of occupational categories, and the rise of identities organised around other characteristics.
Others argue that class has become less visible while remaining determinative, since inequality of wealth has risen in most developed economies since the 1980s, and that the decline is in class consciousness rather than in class.
Health outcomes are among the strongest evidence for continued relevance. The social gradient in health, in which mortality and morbidity vary continuously with position rather than only at the bottom, has been documented repeatedly and is not explained away by behaviour or access to care.
Class is the single variable that predicts the widest range of outcomes, including life expectancy, health, educational attainment, and exposure to the criminal justice system, and it does so across every society where it has been measured.
Its measurement is also unusually consequential, since which definition is used determines what appears in official statistics, and therefore what a society can see about itself.
