The adults of quaint St. Petersburg see themselves as a law-abiding, church-going, family-based group that must police its children. The most respected figure in the novel is Judge Thatcher, who is in charge of administering the law. Virtually every villager shows up to church on Sunday, so that community is formed through an agreed upon set of moral values. The education of the village's children consists largely of learning to follow inflexible rules that are intended to protect these values. The adventures of Tom and his friends often reveal gaps in the adults' logic and inconsistencies in their behavior, with the adults saying one thing but acting otherwise. For example, Aunt Polly tries to force herself to consistently punish to Tom for his rule breaking. But she often compromises herself by administering a lesser punishment, such as tapping him on the head with her thimble when she had originally threatened to whip him with her switch. While Tom is often punished for being untrue to his word, Aunt Polly is not, but remains a moral authority. Twain uses the playful games and interactions of children to also humorously reflect hypocrisy on the broader scale of 19th-century American society and its religion, temperance movement, medical beliefs, and social snobbery. Aunt Polly's belief in "quack" medicines isn't that different from Tom's in black magic, for instance, but medical authorities support her superstitions. To take another example, when Tom briefly joins the Cadets of Temperance, he is motivated by the social status he'll gain in wearing a fancy sash rather than any conviction about the ills of substance abuse. Surely the adults involved in the temperance movement are similarly motivated.
Even if Twain is cutting in his dismissive attitude toward abstract social causes that involve hypocrisy, he sees it as an inevitable and condonable aspect of life in a community. Adults fail to follow through on their word regarding the several adventures Tom undertakes that involve his leaving the village. In running away to Jackson's Island, getting lost in the cave, and tracking down Injun Joe's treasure, Tom and his friends break serious rules, yet in each case the villagers welcome the children home again without punishing them. The adults can hardly be condemned for their hypocrisy in desiring the children's safety, which underscores Twain's belief in the ultimate goodness of community. The individual who does deserve punishment in the novel is the villain Injun Joe, whose desire for revenge against both Dr. Robinson and the widow Douglas reveal that he is incapable of forgiving others, or bending the rules as a hypocrite might. Hypocrisy is a complicated issue in Twain's depiction of St. Petersburg, for the flawed logic it involves is worth noting, but hypocrisy is ultimately a very human, even necessary flaw.