The Adventures of Tom Sawyer: Theme Analysis

Moral growth and maturation
During the first part of the novel, Tom indulges in many pranks and adventures, giving little consideration to the consequences. Fortunately, those consequences never seem to be more serious than causing annoyance to authority figures. Everything changes when Tom and Huck witness the murder in the graveyard and Injun Joe frames Muff Potter, who is innocent of the crime. Suddenly, the boys' actions could make the difference between justice being done or an innocent man being hanged. Tom at first remains silent but has to appease his conscience by taking small gifts to Potter in jail. This shows some moral growth, but not sufficient to quiet Tom's bad conscience. This thread is finally resolved when Tom testifies against Injun Joe. Doing the right thing has overridden his fears for his personal safety. Tom's reward is the adulation he receives from the local people.
Other incidents fuel Tom's growing sense of right and wrong, notably his realization of how badly he has hurt Aunt Polly by staying on the island without telling her he was alive. He resolves this situation by reassuring her that he cares about her, and she forgives him. That Tom matures through this episode is clear when he selflessly takes on Becky's punishment in school - even after Becky has been rude to him. His development continues when despite his irresponsibility in getting himself and Becky lost in the cave, he keeps his head, selflessly looks after Becky, and gets them both out unscathed, once again finding himself lauded as a hero.
The culmination of the 'Injun Joe' and 'courtship of Becky' threads is Tom's discovery of the treasure in the cave. An ordeal involving the hero's journey into a cave or labyrinth is an ancient convention of many 'coming to manhood' stories. The treasure is both Tom's reward for proving that he is worthy of the status of a man and, more prosaically, a symbol of the adult economic system which he is now entering.
Huck also undergoes a moral growth. For most of the novel he is concerned with the necessarily selfish business of survival, but one night he finds himself alone when the time comes to track Injun Joe. When he finds that Injun Joe intends to attack the Widow Douglas, he recalls her kindness to him and commits an entirely selfless act, alerting Mr Jones and thus saving her from Joe.
Subsequently, Huck allows himself to be persuaded by Tom to give up his freedom for a life of being civilized by the Widow Douglas. Some critics say that Tom's championing of conformity, and Huck's grudging acceptance of it, mark both boy's maturation. This interpretation depends on equating respectability with maturity - something that Twain satirizes in the townsfolk. Others view the boys' conversion as a sad capitulation or a failure of imagination on Twain's part (he did not know what else to do with Tom). One thing is certain, however: the boys' final subjection to the restraints of civilization is a necessary rite of their passage into adulthood and into society.
The traditions and conventions of romantic adventure fiction
Tom is an avid fan of romantic adventure stories, such as those of Robin Hood, pirates and robbers. He and his friends give each other such names as "the Black Avenger of the Spanish Main."Tom remembers the plot and even long sections of dialog of such stories in detail, and regurgitates them faithfully in play-acting with other children. This is the more remarkable in a boy who is unable to memorize even a single Bible verse. He is preoccupied with pirates who steal money and kill people - though not they do not kill women, because they are "too noble."
The stories prefigure the 'real life' events that befall Tom: he witnesses Injun Joe's robbing of a grave, attempted extortion, and murder. When Injun Joe's accomplice begs him not to kill the Widow Douglas, Joe replies that killing is not the way to get revenge upon a woman: "you go for her looks. You slit her nostrils - you notch her ears like a sow's." Like Tom's pirates, Injun Joe will not kill women. But in a departure from the romantic tradition of the fictional pirates, Injun Joe's motive for stopping short of killing women is not nobility, but a more exquisite form of revenge.
One implication is that fiction to some extent mirrors real life but is ultimately less tidy and high-minded than fiction. But these romantic conventions may have another purpose in the novel. The criminal activities that Tom and Huck witness are horrific, but they do not seem overwhelmed or traumatized by them. In part, this shows the more casual attitude towards children's psychology in Twain's time. But it is also possible that Tom and Huck have been psychologically prepared by play-acting the stories of pirates and robbers.
Just as Tom's favorite stories often culminate in the hero's discovery of treasure, so does his own story. This is a pleasing, if somewhat unbelievable, meeting of the romantic adventure story tradition and Tom's 'real life.'
Freedom
Throughout the novel, freedom is equated with standing outside society's rules. Good behavior, as defined by adults, means a loss of freedom. It means whitewashing the fence on Saturday, having to while away tedious hours in school, church and Sunday school, and dressing in ridiculous and restrictive clothes like those of the new boy whom Tom beats up for being overdressed. Huck, who does not have to do any of these things because there is no one to tell him to, is admired by the other children as a symbol of freedom.
Tom occupies a position between the free and the imprisoned. Under Aunt Polly's orders, he attends school, church and Sunday school. But whenever he can, he escapes, most notably to the island, where he lives with Huck and Joe Harper as a pirate. Paradoxically, Tom defines his leisure activities with his own strict rules: there are things that are done and not done by pirates and robbers; and Tom's superstitions demand absolute adherence to correct procedure.
The pursuit of freedom, however illusory, has its price, as when Tom upsets Aunt Polly by his staying on the island without telling her he is alive. Tom's growing sense of responsibility, combined with his discovery of the treasure, makes him give up at least some of his wild ways and submit to the restrictions of society. However, he still intends to set up a robbers' gang, which naturally has strict rules about who may and may not join: tellingly, only "respectable" people are allowed in.
The fact that Tom begins the novel admiring Huck for his life of freedom and ends it persuading him to give up his freedom shows that he has accepted that life has to be led with due consideration of the effects of his actions on wider society.
Society's outsiders
Huck, Muff Potter and Injun Joe all live to varying degrees on the fringes of society. Huck, being the son of the town drunk, has no parental authority figure to tell him what to do. His lawless, idle lifestyle makes him "the juvenile pariah of the village," hated and dreaded by the mothers, and admired by the children.
After Huck saves the Widow Douglas from being maimed by Injun Joe, he is welcomed into society as a hero. The Widow intends to keep him within society's fold by housing and educating him, and finally setting him up in business. Huck's story shows that outcast status is not a fixed state, but is fluid, because of society's forgiving nature. Tom too is a beneficiary of this social fluidity, moving from a much-disapproved of status to that of a hero through a mixture of theatrical sensibility and a genuinely heroic and selfless streak.
Muff Potter, another drunk, is also taken back into society's embrace after his innocence becomes apparent. Though guilty of grave-robbing, he is essentially kind-hearted and, we feel, deserving of indulgence.
This deserving ability does not, however, apply to Injun Joe. While his "half-breed" race (half native American, half Caucasian) undoubtedly plays a dominant part in his outcast status in a slave-owning, racist society, he does nothing that remotely merits indulgence or forgiveness. Prepared to kill and maim people for slight reasons, he has a malevolent heart. But in spite of the fact that he is believed to have killed five townspeople, a group of "sappy women" petition the governor to pardon him. Here, Twain satirizes the unreasoning and sentimental sectors of society that fail to discriminate between those deserving and undeserving of forgiveness. Fortunately, Injun Joe's death puts a stop to the petition for pardon, with fate, rather than human wisdom, ensuring that justice is done.
Forgiveness
From the beginning of the novel, a tension is set up between discipline and indulgence, condemnation and forgiveness, regarding the relationship between Aunt Polly and Tom. She says, "Every time I let him off my conscience does hurt me so; and every time I hit him my old heart 'most breaks." The conflict is between head and heart, or duty and love. She seems not to want to discipline Tom too severely, perhaps because part of her sympathizes with his free spirit.
The theme of condemnation and forgiveness is taken up as it applies in wider society. Huck moves from being an outcast to being a hero for saving the Widow Douglas. Tom moves from being viewed as a mischievous child, also to a hero, for his part in saving Muff Potter from being hanged for a crime he did not do, as well as for his theatrical entrance at his own funeral. Muff Potter himself is taken back into society's embrace in spite of his faults and petty criminal tendencies: the fact that he means well counts for much.
In general, Twain presents this tendency towards forgiveness as a beneficent aspect of society. Though he mocks society's "fickle unreasoning" in its U-turn in attitude towards Muff Potter, he adds, "But that sort of conduct is to the world's credit; therefore it is not well to find fault with it" (Chapter 25).
Only once is forgiveness taken to absurd extremes: a group of "sappy women" sentimentalize Injun Joe, a man who has probably killed five people, and want him pardoned. Injun Joe does not deserve forgiveness because he shows no remorse for his crimes and holds only malice in his heart. The women are rightly foiled in their aim by Injun Joe's death.
Hypocrisy
In this novel, all of society's great institutions are present in microcosm, and all are satirized: public morality, the law, education, religion, medicine, and economics.
Twain's beginning assumption is that institutions and the people who represent them should be what they seem. If there is a gap, they are a fair target for satire. If a tavern is a Temperance Tavern, then it should not have a secret whisky den. A Sunday school is supposed to inculcate scripture and Christian values in children, not to enable children and teachers to "show off" before Judge Thatcher. Judge Thatcher, as the highest representative of the law in the county, should not be "showing off" at all, least of all in the Sunday school. Churchgoers should be more interested in the sermon than in the antics of a bug. Schoolteachers should be concerned with the education and well-being of the children in their charge; they should not, as Mr Dobbins does, flog the children in a desperate attempt to make a good showing on "Examination" day and get drunk before the event. The medical establishment should not hype the latest 'cure' at the expense of honesty and concern for the patient's well-being. Finally, society's equating money with status is questioned. It is suggested that society should evaluate people for what they are, not how much money they have; after Tom and Huck come into their money, the townspeople suddenly begin to see the profoundest sense in all their sayings, which they previously ignored.
Twain, often helped by his child characters, punctures the self-delusion of each of the hypocrites, revealing them for what they are - from the collection of grown-up children giggling in the church at the bug, to the sad, undignified, drunk and de-wigged Mr Dobbins.