In 'Introduction: "What Is Literature?"' Eagleton discusses the definitions of literature offered by various perspectives and synthesizes their various arguments to derive a definition of what literature is that satisfies his particular understanding of literature. Three focal points of his discussion are the definitions expressed by the critical theories of Formalism and Marxism and a combined Reader Response and Culturalism.

Reader Response and Culturalism put the reader and the cultural experience first in the definition of literature. In these critical approaches, what defines literature are the reader's interaction with the text and the cultural interaction with the text. Eagleton points out that while these theories validate the idea that literature is not an immutable, not an unchangeable, classification of a work or a cannon of works, the theories cannot conversely invalidate the idea that literature may not be selected by whim based upon personal taste.

Marxist theory defines literature as part of the superstructure, comprising the economic and ideological base of a society, that creates and maintains the power structure that is sustained by literature, art, religion and philosophy. Ideologies, Eagleton points out, are deeply ingrained in social belief about what society is. Therefore, literature sustains the ideology. Writing that does not sustain the ideology of society is rejected, along with the author, and not recognized as contributing to the cannon. Eagleton points out that societies are not homogeneous, are not all uniformly structured with the same ideologies, thus not all sub-sets of society or societies as a whole will accept the same writings as literature because some will violate various foundational and deeply rooted ideological superstructures.

Formalism theory starts to define literature by separating text from the author and from society. This leaves only the text and the structure, the form, of the text from which to derive a definition for literature. Formalists posit that literature makes reality more real through defamiliarization and internal literariness, both of which are embedded in the formal structure through various literary devices. Eagleton points out that authors who wrote would be surprised that their intention and their subjects are irrelevant to the study of their work.

Eagleton's conclusion of this discussion is that though literature is not immutably fixed and while author intention and message remain significant to literature regardless of equal importance of formal issues, the ideological foundations of societies and sub-sets of societies will reject or accept texts based on intention and meaning and based on how texts sustain and support the ideologies that create and support the accepted power structure. Eagleton posits that because, by his definition of literature, literature is writing that uses language in ways that "violently" diverge from the common usage of language in ordinary conversation, meaning represents the accepted appearance of reality. Since the accepted appearance of reality represents the economic base and ideological superstructure that comprises the ruling power structure, texts are literary because the fine, though violently divergent, language supports and maintains the governing power structure.