Near the beginning of the novel, Kingsolver introduces the reader to Tig and Zeke's argumentative and intellectual sibling dynamic during a heated discussion over a family dinner. At some point in the conversation, Tig brings up Zeke's work. She feels he's participating in immoral structures of power that are harming society and the planet, and she makes her point using biting verbal irony:
"But it worked out. The name of our firm is Good Money."
Wow, thought Willa. Grief compartmentalized.
"As in throwing good money after bad," Tig offered.
"As in the fastest-growing sector of personal finance management. Microloans, fossil fuel-free bundles. Socially responsible investments."
"Keep telling yourself that. Helping rich people get richer is socially responsible."
The final line in this passage is a particularly fervent and clear example of verbal irony. Tig says exactly the opposite of what she means—a mechanism to convey that she thinks Zeke is being ridiculous. It's an example of their sarcastic and heated dynamic: they toe the line between joking with each other and insulting each other, yet do so in a manner that also amounts to real, informed debate about fundamental values. Their ironic relationship is a great portrait of a confrontation between two conflicting ideologies and an example of the way humor is sometimes used for ideological sparring.
In Chapter 5, Willa sets out on the long drive from Vineland to Philadelphia to bring Nick to a hospital in the city. After conversing with the rude and grouchy Nick for a while, Willa is tense and frustrated. When she's already in this mood, she has to drive across the Walt Whitman Bridge from New Jersey to Pennsylvania, and a combination of traffic, Nick's comments and radio station of choice, and construction noises frustrate her even further. In this context, she ironically quotes a fragment of Walt Whitman's poetry:
The jackhammer now seemed to be operating directly on her skull. So this is how it turns out, she thought. Hell is the Walt Whitman Bridge. I hear America singing! Singing with open mouths their strong melodious songs!
These lines are from Whitman's poem "I Hear America Singing," in which Whitman celebrates the vigor, industriousness, and vitality of America. The allusion is full of situational irony: Whitman's confidence and joyful patriotism are in fact the opposite of Willa's experience crossing the Whitman bridge. Kingsolver paints a portrait of modern America that clashes starkly with Whitman's idealism.
This clash is heightened by the line "hell is the Walt Whitman Bridge." The form of this line comes from the popular saying "hell is other people," which Willa also quotes elsewhere in the novel. This saying originates in the work of Jean-Paul Sartre, an existentialist philosopher who believed that the world is inherently meaningless and that people must therefore create meaning for themselves. The contrast between this outlook and Whitman's strident patriotism matches the contradiction between the modern reality of the Walt Whitman Bridge and its lofty name. It also captures the feeling of Willa's dry disappointment at the state of America, so different than the dream she believed in for so long.
About two-thirds of the way through the novel, Nick is on death's door. Willa and Iano are grappling with the impending loss of a major figure in their family while also aware that caring for him has been a major toll. To deal with the complexities of these simultaneous truths, Willa uses verbal irony:
They could relax. Dusty wasn't likely to die on them in the night.
Nick was.
"This is why we have families," Willa explained in the darkness of Nick's room. "So we never have to go a single day without worrying ourselves sick."
In this passage, Willa says something obviously untrue for the sake of humor and catharsis. By joking about Nick's condition, the family has an easier time dealing with both their grief and the load of caring for him. This kind of humor is a pattern throughout the novel, and a core facet of Willa and Iano's relationship. It's also applicable to broader themes, like financial hardship or climate change: often, humor is a productive way to not only process information, but to understand the nuances of an issue or theme.
This instance of irony also is only a thin veil over the fact that Willa cares deeply about family. She's found ways to make it more manageable, but her sarcasm reveals the extent to which she is invested in the people around her.