Dennis Gilbert (sociologist) in the context of Bremerton, Washington

The underclass is the segment of the population that occupies the lowest possible position in a class hierarchy, below the core body of the working class. This group is usually considered cut off from the rest of the society.

The general idea that a class system includes a population under the working class has a long tradition in the social sciences (for example, lumpenproletariat). However, the specific term, underclass, was popularized during the last half of the 20th century, first by social scientists of American poverty, and then by American journalists.

Though the American middle class does not have a definitive definition, contemporary social scientists have put forward several ostensibly congruent theories on it. Depending on the class model used, the middle class constitutes anywhere from 25% to 75% of households.

One of the first major studies of the middle class in America was White Collar: The American Middle Classes, published in 1951 by sociologist C. Wright Mills. Later sociologists such as Dennis Gilbert commonly divide the middle class into two sub-groups: the professional or upper middle class (~15-20% of all households) consisting of highly educated, salaried professionals and managers, and the lower middle class (~33% of all households) consisting mostly of semi-professionals, skilled craftsmen and lower-level management. Middle-class persons commonly have a comfortable standard of living, significant economic security, considerable work autonomy and rely on their expertise to sustain themselves.