Eagleton is a socialist critic, and in this groundbreaking book, he argues that all literary theory is ultimately political. Like Barthes and other socialists, he grounds reality in lived history. For Eagleton, there is no ethereal space of "pure" criticism that is "universal," floating above and transcending the historical. He argues that those like the New Critics of Cambridge University in the 1920s and 1930s, who tried to examine literature as a "science" of plots, themes, symbol, ambiguity, and other literary analyses divorced from the historical and political, were themselves political.

In contrast to the New Critics and the formalists, who tried to float literature in a space "above" the historical, Eagleton's introduction firmly ties literature as an academic discipline to particular historical changes. Most specifically, he links the growth of the field to the rise of the working class and night-school universities that arose in England in the late nineteenth century to educate the laboring classes. Since this group did not know Latin and Greek, the traditional Oxford-style university core curriculum was not possible to implement. English literature became a substitute for the classics.

Eagleton, in his introduction, argues that how literary criticism contextualizes literature is ideological: literary theory most often fits literature into a framework that reinforces the power of the elite groups that control society. By positing that literature expresses "universal" and "unchanging" values, for example, critics promote the ruling-class ideology that the way things are now is the way they always have been and always will be, which works against social change. In this book, Eagleton will argue for other ways of understanding literature.

Eagleton wants to define literature for us, and he initially defines it not as the distinction between fact and fiction, but as the use of language in a way that is novel and transformative. He traces this way of thinking about literature as the application of linguistics to the Russian Formalists. The Russian Formalists saw literature as a kind of deviation from the norm.

However, Eagleton writes that this way of thinking about literature is also problematic. Literature's significance is not derived entirely from how it is written, the relevance and truth of its content are also important. Therefore, literature cannot be defined objectively and is dependent on the way in which people read it. Literature is not defined by its inherent characteristics but by "the ways in which people relate themselves to writing," in Eagleton's words. Literature is writing that relates to the complexity of modern life and that people place a high value on. Literature may or may not be fine writing (as there is bad literature), but it is, in Eagleton's words, "a highly valued kind of writing." The consequence of this definition is that it is not objective. While the definition of literature is subjective, it is not, in Eagleton's words, "whimsical," as it is rooted deeply in social ideologies. That is, our history and culture help us define what is considered literature. 

Eagleton's "Introduction" addresses the question made necessary by the study of literary theory, which is a system or systems for critically understanding literature. Eagleton wants to explain the answer to the question "What is literature?" Let's look at how he answers this question and at what his conclusion is.

To answer "What is literature?" Eagleton examines several different ways of defining literature and points out the difficulties with each of them. He says that Russian formalists reduce everything in a work of literature to the formal, that is structural, parts of the text and equally disregard author and message. He mentions that Formalist Osip Brick once said, in defence of disregarding the author when analyzing literature, that if Pushkin had not lived, Eugene Onegin--which is the textual expression of a material reality--would have been written anyway because it was a textual expression of a present material reality.

Eagleton points out the difficulty with this definition of literature by explaining that a past author, such as Orwell, would be surprised that the subjects and themes they wrote about were not important, but rather the literary devices that upturn reality through "defamiliarization" and other devices, which give a work "literariness," are what is important. 

He also presents the definition that literature is that which is chosen as "fine writing" based on social value-judgements. He discusses how, according to Marxist theory, these value-judgements arise from the ideologies that form the superstructure that create and uphold the power structures in society. The difficulty he points out here is that society is not homogeneous, thus an expected social value-judgement may not be forthcoming when a work is presented as being representative of the social ideology thus leading the work (and author) to be rejected.

With these and many more discussions and examples of proffered answers to what literature is, Eagleton arrives at his definition and at what he wants to explain. In brief, Eagleton concludes that:

• (1) literature is not objectively determined: that which is called literary may not remain immutably, unchangeably categorized as literature.

• (2) literature is not a construct of "whimsical" choice on arbitrary principles of "taste."

• (3) literature presents linguistic expressions of social and personal representations of beliefs within non-homogeneous social ideologies which holds "literary language as a set of deviations from a [conversational] norm."

• (4) literature is derived from strong undercurrents of social ideologies representing strongly rooted (often invisible) belief systems.

• (5) literature supports the "assumptions" of the social ideologies by which select groups "exercise and maintain power" over the social construct

Eagleton ends by suggesting that his assertions can be proven and chooses the history of English literature as a starting place for that proof (Chapter 1: "The Rise of English").

[S]ocial ideologies ... refer in the end not simply to private taste, but to the assumptions by which certain social groups exercise and maintain power over others. If this seems a far-fetched assertion, a matter of private prejudice, we may test it out by an account of the rise of 'literature' in England.