Many different types of lies show up throughout Huckleberry Finn. First and foremost, the two main characters—Huck and Jim—lie about their identities in order to protect themselves. As Huck is on the run from his abusive father, Pap, and Jim is trying to escape being recaptured into slavery, lying is what keeps them safe. At one point, Huck dresses up as a girl in order to gather information in town about if people are still looking for him and Jim. As he gets to know Jim better, he begins to lie simply to keep Jim safe, like telling the duke and the king that he is Jim's enslaver or making up a story about a smallpox outbreak in order to get slave-catchers off their trail.
The duke and the king also tell lies, but of a different kind. As con men, they lie about all sorts of things in order to get what they want: they tell Huck and Jim that they are royalty in an attempt to earn a space on the raft, scam a grieving family by claiming to be brothers of a recently deceased man, and trick a town of impoverished people into paying for a fake show. Tom Sawyer also tells morally questionable lies. Unlike the duke and the king, he is not trying to extract money from people, but rather trying to have the types of adventure he’s read about in books.
By filling the pages of Huckleberry Finn with lies, Twain encourages readers to decide for themselves which lies are acceptable and which are not. Ultimately, the book paints a portrait of a hypocritical society where morality doesn't necessarily come from truth-telling but from developing one's own moral compass, as Huck successfully does by the end. He no longer believes the lie at the center of pre-Civil War America—that Black people should be enslaved and treated as less than human—and instead acts in the way he thinks is right in each moment in order to protect himself and his friend Jim.