Marx spent his life trying to get the working class to see itself as a real social group with a common destiny. In his terms, they were a class-in-itself, an objective social unit. They were hampered from acting together to advance their common interest, though, because they were divided by a dozen other identities. The workers of the world were not united because they didn't have a class consciousness. The working class was a class-in-itself, but not a class-for-itself.
Peter Laslett was a great British demographer who wrote The World We Have Lost, the definitive quantitative study of late medieval society. There he argued that in late medieval and early modern society, the aristocracy -- that infinitesimal slice of the top of the social structure -- was the only group in society with a class consciousness. Everyone else lived in such a tiny social world that their consciousness only extended to the limits of people they knew personally. He went so far as to call the world we have lost a "one-class" society, since no one else but the aristocrats were a class-for-themselves.
I mention all this because E. Digby Baltzell, whose work I wrote about yesterday, makes an interestingly parallel argument. In Philadelphia Gentleman, he notes that the community studies that were so prominent in mid-20th century sociology -- especially Middletown, the Yankee City studies, and the Elmtown studies -- erred in seeing each class as a class-for-itself. Such studies found that people knew which side of the tracks you were from, and never let you really cross them. Ambitious young people from the lower classes often left town to advance.
The error, Baltzell says, is that these studies took small cities as representative of national class cultures as a whole. Muncie, IN (Middletown), Newburyport, MA (Yankee City), and New Haven, CT (Elmtown) did have a ruling class whose members knew one another and were tied to one another in a dozen ways. The same was true, more of less, of the several classes below the top in these small cities. In a big city like Philadelphia, though, the upper class likewise knew one another and were connected in a dozen ways. But the several fractions of the middle class, and the many fractions of the working class, and the endless fragments of the poor were not unified, not tied together by many interwoven social ties. This was why ambitious rising men and women of the small cities moved to the big city - no one knew which side of the tracks they came from, or really cared.
In Philadelphia, only the upper class could be a class-for-itself.