- The dominance of commodity relations
- The social, political and legal privilege held by the owners of capital
Commodity relations are a specific kind of economic relations, a particular way that people socially relate to each other regarding the use of purposeful human activity to create the "stuff" that we need for material survival and enjoyment.
Under commodity relations, each individual typically produces one or two commodities, such as hats, shoes, coats, wheat, rice, houses, computer programs, movies, and so forth. Individuals then exchange those commodities with other individuals. Furthermore, this exchange is "hostile", in that both individuals in any exchange are trying to get the "best" deal at the expense of each other (thus distinguishing commodity relations from the exchange of gifts).
Commodity relations existed before the capitalist era: people have exchanged the products of their labor since time immemorial, but under capitalism commodity relations are the dominant form of economic relations. People exchanged things under feudalism, but most labor was directed towards individual self-sufficiency (each individual directly consumed most of the products of his or her own labor, without exchange) and the dominant form of social economic activity was paying tribute to the feudal aristocracy and nobility, without a direct and immediate exchange of compensating commodities.
Similarly, although commodity relations dominate under capitalism, not all economic relations are commodity relations. If you do your own housework, that's labor (human activity that's not inherently desirable, but is purposefully and effectively employed towards a desirable end) but you don't exchange the product of your labor with others. (Of course, hiring someone to clean your house is a commodity relation.) Likewise, taxes are not a commodity relation; the benefits of taxation are indirect and deferred, not direct and immediate.
But still, under capitalism, most people spend the majority of their working day producing a single good or service, which they exchange for money, which they exchange for all the various commodities they need for survival and the enjoyment of life. In order to understand capitalism, we have to understand commodity relations in some detail.