After Ursula Iguaran discovers the route to civilization, the village swells and expands with visitors and new settlers. Jose Arcadio Buendia regains his position as the village's most important citizen as the new inhabitants look to him for guidance and assistance in city planning. While Jose Arcadio Buendia supervises the village's growth, his family is also growing. Pilar Ternera gives birth to Arcadio, the missing Jose Arcadio's son, and the child is brought to live with the Buendias. A new member of the family comes in the form of the orphan girl Rebeca, who arrives out of the blue carrying her parents' bones in a bag. Unsure of what else to do with her, the Buendias take her in, and struggle to cure her of the habit of eating earth and whitewash.
Rebeca brings an insomnia plague to the villagea plague that causes everyone to live painlessly without sleep and to lose their memory. It gets so bad that Aureliano has to label everything in the house and, eventually with Jose Arcadio Buendia's help, the town. The plague does not end until Melquiades the gypsy returns. Old, decrepit, and apparently risen from the deadhe claimed being dead was too lonelyhe brings not only an antidote to the plague but also a miraculous new invention, the daguerreotype. The Buendias have their first and only family photograph taken and Jose Arcadio Buendia becomes obsessed with making a daguerreotype of God, in order to prove His existence.
Meanwhile, Aureliano has grown to manhood without knowing a woman. Although the rest of the village thinks something about him is odd, he is content to spend his days quietly and alone, shut up in Jose Arcadio Buendia's alchemy laboratory, where he is an expert silversmith. He shares the lab with Melquiades, who lives with the Buendias and spends his days hunched over mysterious parchments.
Ursula, deeply engaged in a lucrative pastry business, looks up one day and realizes that the house is full of maturing children. Concerned that when they married, they might have to leave for lack of space, she undertakes an enormous expansion of the Buendia house, adding several new wings and rooms. In the midst of the expansion she receives a letter from the newly-arrived magistrate, a representative of the central government who has just set up shop in the formerly independent village. The letter is a decree stating that the house must be painted blue. Furious, Jose Arcadio Buendia drives the magistrate (Don Apolinar Moscote) out of town and, when he re-appears with his family and an armed guard, Jose Arcadio Buendia forces him to submit to the old rules of the village. Thus stripped of his power, Moscote settles into the village with his wife and seven daughters. Aureliano is struck with love for the magistrate's youngest daughter, Remedioseven though the child is only nine years old. Frustrated, he sleeps with Pilar Ternera, who coaxes the secret out of him. Amused and sympathetic, she helps him propose to the girl, who agrees. Eventually, it is arranged with the Moscotes that they will marry when Remedios reaches puberty.
Meanwhile, the two Buendia daughtersAmaranta and Rebecaboth fall in love with Pietro Crespi, a handsome young Italian who comes to install a pianola in the Buendia home. Their passions are intense and make them both sick. Rebeca even reverts back to her habit of eating earth. Eventually, Crespi responds to Rebeca's attentions, but not Amaranta. It is decided that Rebeca and Crespi will marry, although Amaranta declares with a peculiar fervor that this will only happen over her dead body.
In the midst of all this intrigue, Melquiades the gypsy dies. He is the first person to die in Macondothey do not even have a graveyard. Jose Arcadio Buendia burns mercury for two days, as per the dead man's request, and they establish a plot for him with a tombstone inscribed merely with his name. After the mourning period passes, the house seems to be content and peaceful. Aureliano and Remedios are getting closer and he spends several hours a day with the child, teaching her to read. Although Pilar announces that she is pregnant with his child, Aureliano is happy with his future bride. Rebeca and Crespi are engaged. But the good spirits are dampened by the behavior of Jose Arcadio Buendia. After failing to obtain a daguerrotype of God, he throws himself into the quest of putting everything on a pendulum. This final quest exhausts him mentally and psychologically. After seeing the ghost of Prudencio Aguilar and communing with the dead, he goes into a rage, destroying the laboratory and attempting to set fire to the house. It takes twenty men to restrain him, which they can only do by lashing him to a tree. Ursula builds a shelter to protect him from the sun and the rain and he remains there.
The final image of Chapter Foura humbled and defeated Jose Arcadio Buendia, lashed to a treeis a crucial one. Continuing with the Biblical overtones of the book, this tree is meant to suggest the Tree of Knowledge, the tree that was forbidden to Adam and Eve and caused their expulsion from the Garden of Eden. Like them, Jose Arcadio Buendia has overstepped humanity's boundaries with his obsessive quest for knowledge. And like them, his family and his village will be turned out of the Garden, forced to weather plagues (like the insomnia plague) and violence (the magistrate's appearance is a comical foreshadowing of the government "interventions" to come). This novel is as much about humanity's failure to communicate with one another and care for one another as it is about the Buendias.
Accordingly, this section also introduces the crucial theme of solitude that is central to Marquez's project. Note that the word solitude appears frequently throughout the text, even in surprising places and with surprising usages. Marquez does this to underline the importance of solitude in the novel. In part, solitude can be a healthy thingas the village grows and more and more frightening aspects of civilization come to Macondo (absurd governmental regulations, prostitution, etc.), there can be comfort found in one's own company. Certainly Aureliano and Melquiades confirm this. But the solitude of the Buendias, as the novel will make clear, is destructive. The critic Ricardo Gullon points out that the family's incest problem is representative of their greater failure to communicate and reach out to the rest of the world. By having Jose Arcadio Buendia babble in a foreign tongue at the end of chapter four, and using the example of labeling during the insomnia plague, Marquez introduces the unsettling question of what happens to communication when even language breaks down. To what extent do we rely on language for the permenance of memory, Marquez asks, and what happens when we all stop speaking that language? These topics are particularly of relevance to Marquez because of Latin American history, which was notoriously distorted in textbooks when Marquez was a child. He will return to this theme later in the book, when the history of the banana revolt is pushed out of public memory by the actions of the government.