Every known society ranks people in some way. Some ranks are earned, some inherited, some imposed. Sociologists use the term social stratification for a system by which a society ranks categories of people in a hierarchy. Stratification is a feature of society, not simply of individuals: it persists across generations, it varies in form from place to place, and it is always accompanied by beliefs that explain why the ranking is fair or natural.

Caste and class

Stratification systems range from closed to open. In a caste system, rank is assigned at birth and very hard to change. Marriage, occupation and social contact are largely confined within one's caste, and religious or traditional beliefs support the order. The traditional caste system of India and the racial order of apartheid South Africa are the best known examples. In a class system, rank depends partly on achievement. The key contrast is that caste position is fixed by birth, while a class system allows some movement up or down. No real society is purely one or the other: class societies keep many advantages of birth, and caste societies have always seen some movement.

Weber's three dimensions

Marx saw stratification mainly in terms of ownership of the means of production. Weber thought this too narrow and described inequality along three dimensions: class, status and party. Class is economic position: income, wealth and life chances in the market. Status is social honor or prestige: how much respect a group receives. Party is power: the ability to shape decisions, through political parties or any organized group. The three often go together, but not always. A member of the clergy may have high status and modest income; a lottery winner gains wealth without prestige. Sociologists often combine income, education and occupation into a single measure called socioeconomic status.

Is inequality necessary?

In 1945 the American sociologists Kingsley Davis and Wilbert Moore offered a functionalist answer. Some positions, they argued, are more important than others and require scarce talent or long training. The Davis-Moore thesis holds that unequal rewards attract talented people to important positions; without higher pay and prestige, few would endure years of medical school. Defenders note that every complex society has had some inequality and that rewards do motivate effort.

In 1953 Melvin Tumin replied with a sharp critique. The importance of a job is hard to measure: is a surgeon more vital than the sanitation workers who prevent epidemics? More important, inherited advantage keeps many talented people from ever competing for top positions, so stratification can waste talent instead of finding it. And rewards may reflect power, not importance. The debate remains alive in arguments about executive pay and the wages of care workers.

Passing advantage on

The French sociologist Pierre Bourdieu argued that money is not the only thing families pass to children. They also pass on cultural capital: knowledge, tastes and styles valued by schools and elites and handed down in families. A child who grows up with books, museum visits and parents who speak comfortably with teachers arrives at school already fluent in what school rewards. Teachers may read that ease as talent.

Social mobility

Social mobility is movement within a stratification system. Intergenerational mobility compares children with their parents; intragenerational mobility tracks change within one lifetime. Some mobility comes from individual effort, but much is structural mobility: movement caused by changes in the economy's mix of jobs. When twentieth century economies added millions of office and professional jobs, many children of farmers and factory workers moved up because the ladder itself had grown.

A 2017 study led by the economist Raj Chetty measured absolute mobility in the United States: the share of children who earn more than their parents did at the same age, adjusted for inflation. About 90 percent of Americans born in 1940 out-earned their parents, compared with about 50 percent of those born in 1980. Slower growth and rising inequality both played a part. Later work by the same team found that the neighborhood in which a child grows up has measurable effects on adult income.

Worked example: two children, one city

Two children are born on the same day in the same city. Leo's parents are lawyers; Sam's parent works two jobs cleaning offices. Both are bright and curious. Leo's home is full of books, and his parents know how to push for a gifted program. That is cultural capital at work. Sam's school has larger classes and fewer counselors. Davis and Moore would point out that if Sam becomes a surgeon, the high pay will have helped draw him into a demanding field. Tumin would ask how many children like Sam never get the chance. Weber would notice that even if Sam earns a high income, he may still feel like an outsider in rooms where status is set by manners learned in childhood. None of this means either child's effort is meaningless. It means that equal worth at birth does not yet mean equal chances.