In examining works of literature, Marxist literary theorists emphasize the precise economic, social, and historical conditions in which they were written. Whereas more traditional literary criticism pays little heed to these conditions, Marxist theorists maintain that we cannot gain a proper understanding of literature unless we are aware of how and why it is produced.
To that end, Marxist literary theory looks at literature as part of the so-called superstructure of society. In Marxist thought, the superstructure can be defined as the cultural world of art, ideas, and morality that exists in any given society. That world has a symbiotic relationship with the base, which is the economic foundation of society.
To understand the superstructure, which of course would include works of literature, we need therefore to understand the economic base that gives rise to it. To be sure, the relationship between base and superstructure in classical Marxism is reciprocal, but the base undoubtedly plays the main part. It is the base that ultimately determines the superstructure.
A work of literature arises within certain economic and historical contexts. A play or a novel, for example, isn't treated by Marxists as if it were the purveyor of timeless truths, standing apart from the society in which it was created. On the contrary, literature, like morality, and like the culture of any given society, cannot be understood without reference to the economic and historical conditions that give rise to its creation.