Inequality is a central and familiar topic for sociological research (as it is for social and political philosophy). But it is worth probing what kinds of inequality may exist in society and what kinds of explanations might serve to account for these various social processes and outcomes. What do we want to know about social inequalities?
Most evidently we can observe inequalities across individuals and groups with respect to the level of attainment of various important social goods: income, wealth, home ownership, health status, educational attainment, and employment, to name several. It is trivial to observe that there are differences across individuals with respect to these goods -- John has higher income and better health than Phil. What is less trivial is the discovery that members of a group, defined in terms of one or more socially significant properties, show differences with respect to these outcomes: inequalities of income between men and women, inequalities of incidence of diabetes across white and black adults, differences in educational attainment across rural, suburban, and urban residence, and so forth. Once we have identified inequalities like these across social groups, we want to have a causal explanation of the differences. What are the social processes through which these differences in outcome arise?
A related kind of inequality is somewhat less tangible. It has to do with unobservable social properties like status, power, or privilege. We can't directly measure this person's total social power or that person's social status. But we can arrive at comparative judgments about the relative level of status and power for various individuals, and we can likewise make comparative judgments about these qualities as exhibited by various social groups. Once again the question of social causation arises: what are the social processes that give rise to different levels of power, status, or privilege for various social groups?
In each instance we want to know what the social processes and mechanisms are that proliferate outcomes differentially across groups defined by such characteristics as race, gender, income status, etc. What factors and processes cause the occurrence of inequalities with respect to a social good across social groups defined by a socially salient property (race, gender, age)? If there is a measured difference with respect to the social property across two groups, there must be a causal factor that distinguishes the groups. A natural hypothesis is that human talents and personalities are randomly distributed across all human beings. On this assumption, we should expect that there will be no differences of outcome across social groups that are purely based on differences of talent, since by hypothesis there is no difference in the distribution of talents across randomly selected groups. So if there are observed differences in outcome, we need to find a social process that would explain the differences across groups. There must be a causal factor that explains the difference.
We might say that there are only a few basic possibilities. Members of the groups might possess personal characteristics differentially that causally produce the good. This might be the result of filtering or differential recruitment into the group. Second, the mechanisms assigning the good to individuals might discriminate on the basis of the property or a correlated property. Third, membership in the group might give members differential access to resources or opportunities that are themselves productive of the good.
So far we have formulated the problem as one of explaining inequalities across groups defined by some other feature. But there is a separate issue about inequalities that sociologists address. Suppose we notice that the “rich” are gaining a higher percentage of income over time and the “poor” a falling percentage. These two groups are defined with respect to the very property with which they are measurably unequal. Formulated from this perspective, the question is this: what are the causal factors possessed by the group of “rich” that accounts for their high income, and conversely for the “poor”? Upon investigation we might find that the two groups are different in a variety of ways: amount of higher education, place of residence, race, age. This might lead us to ask the question, are some of these factors causal with respect to income; are other factors collateral effects of high income; and are yet others simply the non-causal correlates of the truly causal factors?
This suggests two angles of approach on the question of inequalities across groups. One is to single out the two populations at opposite ends of a particular spectrum of difference and examine their various characteristics. The other is to single out a socially salient property (race, for example) and investigate whether there are differences with respect to the social good (income). The first cut raises the question, what factors distinguish the high-achieving and low-achieving groups that might explain the observed differences; the second asks, why is the property causally relevant to the distribution of the good?