Although Karl Marx called members of the upper class the "bourgeoisie," the two terms are not synonymous. The bourgeoisie are the people who own and control the means of production, not just the upper class. People may be in the upper class if they are wealthy like professional people and shopowners, but they are not part of Marx's bourgeoisie, because they do not own the means of production of good and they don't employ workers in factories.

Likewise, the term "proletariat" does not equate exactly to the "lower class."