How we cite our quotes: (Section.Paragraph)
Quote #1
[The fundamental] proposition is: that in every historical epoch, the prevailing mode of economic production and exchange, and the social organization necessarily following from it, form the basis upon which it is built up, and from which alone can be explained, the political and intellectual history of that epoch; that consequently the whole history of mankind (since the dissolution of primitive tribal society, holding land in common ownership) has been a history of class struggles, contests between exploiting and exploited, ruling and oppressed classes; that the history of these class struggles forms a series of evolutions in which, now-a-days, a stage has been reached where the exploited and oppressed class—the proletariat—cannot attain its emancipation from the sway of the exploiting and ruling class—the bourgeoisie—without, at the same time, and once and for all, emancipating society at large from all exploitation, oppression, class distinctions and class struggles. (Preface.6)
According to Marx, the economic system of a historical period shapes the kind of social organization that economic system needs in order to function. Because humans are primarily beings that make stuff, and because an economic system dictates how they make that stuff, that economic system also dictates how those people arrange themselves socially and politically. What is constant throughout all historical ages is the existence of the proletariat as an exploited class. The only way for the proletariat to be free of this exploitation, Marx says, is for it to completely transform society and erase all class distinctions.
Quote #2
[The proletariat is] a class of labourers, who live only so long as they find work, and who find work only so long as their labour increases capital. These labourers, who must sell themselves piecemeal, are a commodity, like every other article of commerce, and are consequently exposed to all the vicissitudes of competition, to all the fluctuations of the market. (Section1.30)
Proletarians aren't able to thrive as people, because they have to sell off parts of themselves—their labor—in order to survive. This leaves them vulnerable to the instabilities of the market: what happens to workers if no one buys what their labor has made?
Quote #3
The bourgeoisie finds itself involved in a constant battle. At first with the aristocracy; later on, with those portions of the bourgeoisie itself, whose interests have become antagonistic to the progress of industry; at all times, with the bourgeoisie of foreign countries. In all these battles it sees itself compelled to appeal to the proletariat, to ask for its help, and thus, to drag it into the political arena. The bourgeoisie itself, therefore, supplies the proletariat with its own elements of political and general education, in other words, it furnishes the proletariat with weapons for fighting the bourgeoisie. (Section1.41)
Marx is careful not to think of the bourgeoisie as one solid group. He understands that members of the bourgeoisie are constantly in competition with each other, both at home and abroad. For example, a shiny new gizmo for sale will naturally pit its inventor against whoever is selling the previous technology. When this happens, the bourgeoisie will turn to its workers for help in fighting competitors—but this also teaches the workers how to fight the bourgeoisie directly, on their own.