Tristram picks up where the last chapter left off, undertaking now "to explain the nature of the perplexities in which my uncle Toby was involved" in his attempts to tell the story of his war wound. Toby's trouble was that the military maneuvers in question were so intricate and technical that nobody could understand him; indeed he sometimes even confused himself as well. It occurs to him now to get a large map of the environs of Namur, which relieves him of his difficulty and also sets him off on his hobby-horse.
Tristram informs the reader that his book is to be a "history-book" in the same way that Locke's Essay Concerning Human Understanding is a history-book--that is, as a history "of what passes in a man's own mind." He goes on to attribute the obscurity in Toby's battle descriptions not to any kind of mental confusion, but to a confusion in language itself: the "unsteady uses of words" that predominates especially in the technical jargons of specialized fields.
Captain Toby's obsession with his map grows, and he launches into a detailed study of fortification and military science that becomes his ruling passion. He soon grows restless for his recovery. Tristram, after reminding us that he still means to resume the interrupted conversation from Volume 1, Chapter 21 (when he cut Toby off at "I think --"), proceeds with the story of his uncle's sudden desire to leave the sickbed: Corporal Trim, Toby's servant, had planted the suggestion in his master's mind that they should move to the country in order to construct a replica, built to scale, of the battle site and fortifications. This idea pleases Toby so intensely that he can hardly wait to begin.
Tristram resumes the scene by the fireside on the day of his own birth, and Toby finishes his long-delayed sentence by suggesting that they ring the bell to inquire about all the noise upstairs. The labor has begun in earnest; Susannah runs for the midwife, and Walter sends Obadiah to fetch Dr. Slop. Speculating about Mrs. Shandy's preference for the midwife, Toby suggests that it might be a question of modesty. Walter challenges him on this point, and Toby defers, admitting that he knows nothing about women. He alludes to the unfortunate outcome of his affair with Widow Wadman as evidence of the fact. Walter begins to hold forth about the right and the wrong end of a woman, but is interrupted by a knock at the door.
Obadiah and Dr. Slop have arrived. Tristram reflects on the complications of calculating time in a narrative where events are happening simultaneously, or in comparing narrative time with lived time. He first claims that it has been an hour and a half since Obadiah left on his errand--plenty of time to return with the doctor. He then argues, from the other side, that no more than two minutes, thirteen and three-fifths seconds could possibly have passed. Finally, he offers the conjecture that years have passed, since all the stories of Uncle Toby's military career and invalidism have intervened since the birthday was first mentioned. His imaginary critic remains unpersuaded, so Tristram closes the matter by revealing that Obadiah actually ran into Dr. Slop just outside the house, in a collision that sent them both into the mud.
Obadiah is sent back out to fetch the doctor's tools, which the doctor has left at home. Toby has been put in mind of Stevinus, an engineer and writer on fortifications; he explains the connection, which seems illogical to everyone else. Walter insults him for his doggedness and stupidity. Tristram relates that Toby's feelings were hurt, but that he "was a man patient of injuries." He goes on to tell a sentimental anecdote about how Toby "scarce had heart to retaliate upon a fly," and attributes whatever goodwill he himself has learned to the early impression of his uncle's gentleness and humanity. Walter, seeing Toby's serene countenance, quickly apologizes, and the brothers are reconciled. Corporal Trim delivers a sermon on conscience (actually one of Sterne's own) that has fallen out of the volume of Stevinus. Tristram gives a minutely detailed visual description of the stance Trim assumes for this oration. The sermon proves to have been left in the book by Parson Yorick, who subsequently retrieves it.
Obadiah returns with the bag of surgical instruments, and attention turns once again to Mrs. Shandy's labor. Dr. Slop is told that he is not to interfere unless called for, so he contents himself with educating the company about recent advances in the science of obstetrics. We learn about another one of Walter's pet theories: that the medulla oblongata is the most important part of the brain, and that it stands in great danger during the process of childbirth. With strength in numbers, the medical hobby-horses of Walter and Dr. Slop outpace Uncle Toby's militaristic reflections, and the latter is unable to regain the floor. The volume closes with a reminder of certain narrative loose ends still to be picked up, most importantly: how Toby got his modesty from his groin-wound, how Tristram's nose was lost in the marriage contract, and how he came to be named Tristram.
In calling his work a history of "what passes in a man's mind," Tristram draws attention to the fact that, in writing his own "life and opinions," he will be portraying mostly a mental life. This reassurance is important in light of the fact that we have moved through two volumes without yet arriving at the point of the protagonist's birth. He addresses our expectations on this point not only to help us make sense of the work, but also because those expectations are part of what the work is about--as is the question of how exactly the mental life figures in the life of a man. Still, the comparison to Locke's Essay Concerning Human Understanding is a provocative one: does Tristram mean that Locke's highly theoretical book is actually more autobiographical and introspective than philosophical? Or is he suggesting that his own book, however personal it may be, will draw out general truths about human nature? The author problematizes, through considerations like these, the relationship between a history of an individual mind and a philosophical account of human thinking in general.
The comparison to Locke also raises the question of the genre of this text. Sterne's book could be considered a novel; Tristram's narrative is certainly not one. Tristram Shandy actually draws on the conventions of a number of genres, if often only to poke fun at them or turn them on their heads. Ultimately, the novel recasts these conventions into a unique structure of its own. Comedy, essay, and satire are all modes the author regularly takes up. He refers to other literary works, and also pronounces his own work's independence from them. The presence of whole documents from various non-literary disciplines (like the sermon in this volume, and the memorandum in the first) contributes likewise to the generic heterogeneity of the book. The inclusion of these texts also develops a thematic concern about the clash between everyday human life and the world of esoteric scholarship.
We begin to see more clearly, in this volume, that the novel is weaving together two major narrative lines: one is the sequence that involves the pivotal events of Tristram's early existence. The other traces the story of Uncle Toby, from his soldiering days to his hobby-horse and eventually to his lovelife. In this volume, the spotlight focuses on Toby while Tristram hangs suspended in the background, just on the verge of being born. As Tristram reveals more about his uncle's hobby- horse, the reader sees the ridiculous behaviors into which his obsession with fortifications carries him. We also, however, see him as genuinely kind and sympathetic: the famous anecdote of Toby and the fly invites us to empathize with him as strongly as Tristram does. Yet the overly sentimental tones in which the story is presented suggest that Sterne might be poking fun at the eighteenth-century culture of sensibility, into which Tristram's tale squarely falls. With the allusion to Toby's modesty in the first volume, and to his affair with the Widow Wadman in this volume, Tristram is outlining the trajectory Toby's part of the story will take.
Conversation, in these chapters, is governed by dueling hobby-horses. As the male characters compete for the chance to vocalize their various intellectual obsessions, the dialogue degenerates, becoming at certain moments either unintelligible or utterly irrelevant. The real, consequential event that is taking place upstairs is all but forgotten in the stupidity and self-absorption of their discourse. Yet pregnancy becomes a metaphor for these (often abortive) intellectual labors: Tristram speaks of his father's failure "to be safely delivered of" his explanation about women, and he discusses Walter's speculative tendencies in similar terms: "It is the nature of an hypothesis, when once a man has conceived it, that it assimilates every thing to itself as proper nourishment; and, from the first moment of your begetting it, it generally grows the stronger by every thing you see, hear, read, or understand." When Tristram compares Walter's philosophizing with the labor going on upstairs, we are encouraged to think of Tristram's own writing project in the same way. The birth at the center of the novel is a figure for the idea of the "brainchild"--the process of mental construction that is the major subject of the book, and of which the book itself stands as an example.