Moby Dick's structure is in a sense one of the simplest of all literary structures-the story of a journey. Its 135 chapters and epilogue describe how Ishmael leaves Manhattan for Captain Ahab's whaling ship, the Pequod, how Ahab pilots the Pequod from Nantucket to the Pacific in search of Moby Dick, and how in the end Ishmael alone survives the journey. This simple but powerful structure is what keeps us reading, as we ask ourselves, 'Where will Ahab seek out his enemy next? What will happen when he gets there?' Some critics have divided the book into sections, like acts in a play. The first, from Chapter 1 to Chapter 22, describes Ishmael, portrays his growing friendship with Queequeg, and serves as a kind of dry-land introduction to themes-whaling, brotherhood, and man's relationship with God-explored in greater detail at sea. The next section begins as the Pequod sails and continues to Chapter 46. Here you meet both Captain Ahab and, in description if not yet in the flesh, his great enemy, Moby Dick.
A long middle section, from Chapter 47 to Chapter 105, shows the Pequod at work as whales are hunted and killed and other whaling ships met. It also shows Ishmael pondering the meaning of these activities. The plot slows as Melville takes time to gather and display proof of the importance of the Pequod's voyage. Then, from Chapter 106 to the book's end, we " re caught up in the excitement as Ahab steers his ship nearer and nearer to Moby Dick and final disaster. Although Moby Dick's basic structure is simple, the book is anything but simple, in part because Melville writes in several literary forms. As a whole, Moby Dick is of course a novel, but some of its chapters are written as if they were scenes in a play.
The chapters involving Father Maple and Fleece contain sermons. Other chapters, most notable Ishmael's discussion of whales and whaling, resembling essays. Indeed, some readers have compared Moby Dick not to novels but to other kinds of literary works. Some have noted its similarity to epic poems, such as Homer's Odyssey. Like this epic, Moby Dick tells of a sea journey and a battle between men and gods. Other critics see resemblances to Greek or Elizabethan tragedy.
Still others have abandoned literature altogether to liken Moby Dick to a musical symphony or even to the ocean itself. It's the richness contained within Moby Dick's simple structure that accounts for such differences of opinion.