Throughout The Adventures of Tom Sawyer, Aunt Polly threatens to punish Tom for his actions—including threatening to physically beat him—but she rarely does. This is an example of situational irony because readers expect Aunt Polly—as a pious and sincere woman—to follow through on her word.
In an early scene in the novel, Aunt Polly even goes as far as to raise a switch at Tom, but ultimately laughs when he escapes:
The switch hovered in the air—the peril was desperate—
“My! Look behind you, aunt!”
The old lady whirled round, and snatched her skirts out of danger. The lad fled, on the instant, scrambled up the high board fence, and disappeared over it.
His aunt Polly stood surprised a moment, and then broke into a gentle laugh.
Aunt Polly’s laughter here is unexpected—she was furious a moment before, and yet she allows Tom trick her into letting him get away. This therefore becomes one of the examples of adult hypocrisy in the novel, one that Aunt Polly herself recognizes:
He 'pears to know just how long he can torment me before I get my dander up, and he knows if he can make out to put me off for a minute or make me laugh, it's all down again and I can't hit him a lick. I ain't doing my duty by that boy, and that's the Lord's truth, goodness knows.
While Twain uses irony and satire to highlight harmful examples of hypocrisy in the novel, here he approaches Aunt Polly’s hypocrisy with compassion. It’s sometimes necessary for people to be hypocritical, Twain suggests, if it comes to keeping children cared for and safe.
In an example of dramatic irony, Tom convinces all of his friends to spend hours whitewashing Aunt Polly’s fence. This is a chore that readers know Tom was given as a punishment for playing hooky from school, but one that he frames for his friends as a privilege, such as in this conversation with Ben Rogers:
“Oh come, now, you don’t mean to let on that you like it?”
The brush continued to move.
“Like it? Well, I don’t see why I oughtn’t to like it. Does a boy get a chance to whitewash a fence every day?”
To the surprise of readers, Tom’s manipulation is very effective—only a moment later Ben says, “Say, Tom, let me whitewash a little.” By the end of the day, Tom had convinced at least a dozen boys not only to paint the fence but to pay him for the opportunity to do so (via toys and other collectible items). Tom feels no guilt about this, thinking to himself that he could’ve bankrupted the entire village if he didn’t run out of whitewash.
This ironic experience establishes at the start of the novel that Tom knows how to easily manipulate people while avoiding taking responsibility for his actions, setting the scene for his eventual maturation.
In an example of dramatic irony, Tom, Huck, and Joe sneak into the funeral that the village holds for them when all of the townspeople believe the boys to be dead. (In reality, the three of them were secretly living on Jackson’s Island to play pirates and engage in other fantasies.) Twain captures the irony of the moment as he describes the “three dead boys” walking into the church:
First one and then another pair of eyes followed the minister’s, and then almost with one impulse the congregation rose and stared while the three dead boys came marching up the aisle, Tom in the lead, Joe next, and Huck, a ruin of drooping rags, sneaking sheepishly in the rear! They had been hid in the unused gallery listening to their own funeral sermon!
Readers know that the boys are alive and well—they’ve just been hiding on Jackson’s Island—but everyone in St. Petersburgh earnestly believes them to be dead, making this a prime example of dramatic irony.
There is situational irony in this scene as well in that, before Tom, Huck, and Joe entered, the minister was discussing the misbehaving boys as if they were saints:
The minister related many a touching incident in the lives of the departed, too, which illustrated their sweet, generous natures, and the people could easily see, now, how noble and beautiful those episodes were, and remembered with grief that at the time they occurred they had seemed rank rascalities, well deserving of the cowhide.
The irony here is that, as the minister waxes poetic about the “sweet, generous” boys, the very same boys are actively manipulating everyone in town, engaging in the type of “rank rascalities” of which the minister was is trying to absolve them.
For a brief time, Tom joins the Cadets of Temperance, a group of children who were—historically speaking—part of the anti-alcohol temperance movement. The situational irony is that Tom doesn’t join for any principled reasons, but because he wants to wear a sash:
Tom joined the new order of Cadets of Temperance, being attracted by the showy character of their “regalia.” He promised to abstain from smoking, chewing, and profanity as long as he remained a member […] Tom soon found himself tormented with a desire to drink and swear; the desire grew to be so intense that nothing but the hope of a chance to display himself in his red sash kept him from withdrawing from the order.
As the quote also makes clear, there is a second layer of irony at play here: Tom has no interest in smoking or cursing until he commits to not doing these things. In classic Tom fashion, he must rebel against any form of authority with which he comes in contact. The irony of his behavior only increases when he quits the cadets and finds his interest in these rule-breaking activities reversed:
The Cadets paraded in a style calculated to kill the late member with envy. Tom was a free boy again, however—there was something in that. He could drink and swear, now—but found to his surprise that he did not want to. The simple fact that he could took the desire away, and the charm of it.
Once again, Tom proves that his primary motivation in life is to break rules, indicating the degree to which he has not yet matured. He will do so over the rest of the novel, of course—ultimately coming to accept the norms of adult society.
In an example of situational irony, Tom makes Huck swear that neither of them will reveal that they saw Injun Joe kill Dr. Robinson, and then he promptly turns around and testifies in court saying exactly that. When Tom asks Huck to promise that he will not tell the truth, he is extremely serious about it (making Huck swear with “dread solemnities”):
“Huck, they couldn’t anybody get you to tell, could they?”
“Get me to tell? Why, if I wanted that half-breed devil to drownd me they could get me to tell. They ain’t no different way.”
“Well, that’s all right, then. I reckon we’re safe as long as we keep mum. But let’s swear again, anyway. It’s more surer.”
So they swore again with dread solemnities.
After this scene, Twain intentionally keeps readers in the dark about the fact that Tom has gone against his promise to Huck and told the lawyer he wants to testify. This is Twain's attempt at ensuring that readers feel the full weight of the ironic twist. When Tom is called to the stand by the lawyer, readers inevitably feel the very same “puzzled amazement” of the rest of the villagers:
A puzzled amazement awoke in every face in the house, not even excepting Potter’s. Every eye fastened itself with wondering interest upon Tom as he rose and took his place upon the stand.
The irony of this moment is not just meant to entertain readers, but to show them that Tom is maturing and making tough moral choices, even if they betray the promise he made to his friend and put him into danger. Despite the fact that Huck will be disappointed and Injun Joe will turn his wrath against Tom, he cannot let an innocent man be punished for a crime he didn’t commit.
Despite the fact that Injun Joe is a known murderer, a group of women from the village draft a petition to the Governor to pardon him—an example of situational irony. Readers expect the village to stand behind the families of the victims, but, instead, they go into “deep mourning”:
The petition had been largely signed; many tearful and eloquent meetings had been held, and a committee of sappy women been appointed to go in deep mourning and wail around the Governor, and implore him to be a merciful ass and trample his duty underfoot. Injun Joe was believed to have killed five citizens of the village, but what of that? If he had been Satan himself there would have been plenty of weaklings ready to scribble their names to a pardon petition, and drip a tear on it from their permanently impaired and leaky waterworks.
Here, Twain is highlighting (and satirizing) the hypocrisy of people whose sense of morality is warped. Rather than truly acting morally (by caring for the people who were affected or thinking of the good of the town), these women want to perform a certain kind of piousness that is more about being seen as moral and caring rather than actually being so.
Twain also uses verbal irony to communicate his critical judgment of these attention-seeking grievers, describing how they would seek a pardon for “Satan himself.” He does not believe this, of course, but he uses sarcasm to make clear his critical assessment of them.