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.
