The unconventional structure of The Grapes of Wrath, in which the narrative chapters are interspersed with intercalary chapters of general comment or information, has frustrated and annoyed readers right up to the present day. Many complain that the chapters are interruptions in the story proper, or that they split the novel into two distinct sections only loosely related. The discerning reader, however, will agree with Steinbeck's claim that the structure of the novel was indeed carefully worked out. Employing a variety of literary styles and techniques, Steinbeck is able to cross-reference details, interweave symbols, and provide outside commentary on narrative events in such a way that the two types of chapters blend together, unifying and enhancing the social and humanist themes of the novel. According to Steinbeck scholar, Peter Lisca, the author uses three specific literary devices to minimize disruption and bring together the two components of the novel: juxtaposition, dramatization, and a variety of prose styles.
One technique used to unify the separate parts of the novel is juxtaposition. Details are consistently and repeatedly inter-related between narrative and intercalary chapters. Most often an intercalary chapter will present a generalized situation that will either become more fully realized or brought to a conclusion by the events in the succeeding narrative chapter. For example, Chapter 7 provides the monologue of a used car salesman and is followed in Chapter 8 by an account of the Joads preparing to leave, having just purchased a used Hudson Super-Six. Similarly, Chapter 29, which describes the relentless rains that flood the California valley, is framed by the first drops of rain falling at the end of Chapter 28 and the floods that threaten the Joads' boxcar in Chapter 30. The repetition of key elements, often symbolic or thematic in nature, also works to integrate the two types of chapters. The land turtle, whose symbolic struggle across the highway is meticulously described in Chapter 3, is picked up by Tom Joad in Chapter 4 and released in Chapter 6, only to continue its journey in the direction soon to be followed by the Joad family. In the same way, the family rescued by the benevolent stranger at the end of Chapter 9 foreshadows the "rescuing" of the Wilsons by the Joads in the next chapter.
A second technique, perhaps most widely used in the intercalary chapters, is that of dramatization: The use of a collage of vignettes, monologues, and dialogues designed to show the social and historical processes behind the events that were occurring in the story of the Joads. In Chapter 9, for example, we hear the frustrations of the farmers forced to sell their belongings through an economic system they don't understand, strengthened with the repeated comment, "Can't haul 'em back." Similar to medieval mystery plays that brought biblical stories to life for the understanding of the common people, Steinbeck uses generalized characters and dialogue to illustrate the plight of the dispossessed tenants. Not wishing to merely tell about social or historical facts that composed the backdrop of his plot, Steinbeck allows his readers to find out for themselves the effect of the drought on the sharecroppers, or the gradual deterioration of the houses abandoned by farmers forced to migrate westward.
The dramatically differentiated prose styles used in the intercalary chapters allows Steinbeck to soften the chapters' somewhat moralizing tone and avoid the accusation that they could be grouped together as their own separate section of the novel. The newsreel style of a contemporary of Steinbeck's, author John Dos Passos, is seen in the used car salesman chapter, while the depiction of the boy and his Cherokee girl dancing in Chapter 23 is almost cinematic. The earthy, folk language employed by the Joads, Wainwrights, Wilsons, and other characters in the primary narrative is echoed in the comments of the generalized characters in the intercalary chapters. In keeping with the purpose of these chapters as general expansions of specific events, however, quotation marks indicating precise speakers are quite obviously absent. These conversational collages strengthen the function of these intercalary chapters to provide an overview of the social situation affecting the Joads.