In simple terms, a Marxist would say that all aspects of a culture work to keep the dominant class in power. Culture is caused by economic relations and helps to keep those economic relations in place.
To Marxists, society can be broken up into two parts: base and superstructure. The base of a society consists of all the things that are used to produce goods and services and the ways in which people relate to those things. For example, then, we could say that the base of our society consists of the fact that the means of production are owned by private individuals and that the people who own the means of production hire other people to work for them. This is a very simplified way description of our economy, but it will do for our purposes here.
Marxists would say that all other aspects of our society—all the things we would call culture—grow out of the base. These things are called “superstructure” in Marxist thinking. All aspects of our culture exist, in this view, because they help to keep the dominant class in power. For example, a major aspect of our culture is our belief in individualism. We believe that people have individual rights and that people are responsible for what happens to them. One example of this is how we believe that people’s actions determine whether they become successful in life. Marxists would say that this cultural belief arises because it helps maintain our capitalist system. Because we have this belief, we do not think that it is bad for some people to be poor. We do not think that it is bad for a very few people to have tremendous amounts of money while so many others live paycheck to paycheck, or worse. Our culture leads us to believe that both the rich and the poor deserve to be in their respective positions in life. Therefore, we do not question the basic economic relations that exist in our society.
In short, then, Marxists believe that culture is part of superstructure. It comes about because it helps to maintain the economic power structure of our society.