The first words spoken by Tom Sawyer in The Adventures of Tom Sawyer are a lie. Aunt Polly is looking for Tom and calling out his name. When she eventually discovers him hiding in the closet and asks what he is up to, he blatantly lies by saying, "Nothing." She notices the jam smeared on his mouth and hands and questions him about it, to which he responds with another clear lie, "I don't know, aunt." This introduction paints Tom as a mischievous boy who often gets into trouble. However, Aunt Polly's laughter at his escape from punishment indicates that his deceit and misbehavior are of little concern to her. Throughout the novel, Tom often lies about his whereabouts and activities, mainly to avoid getting into trouble. Nevertheless, when honesty is crucial, Tom understands the importance of being truthful.

After returning home from his pirating adventure, Tom feels guilty for causing Aunt Polly distress with his prolonged absence, so he concocts a story about dreaming of her while he was away. When Aunt Polly later learns that the dream story was untrue, Tom realizes that "what had seemed like a good joke before, and very ingenious ... merely looked mean and shabby now." His conscience ultimately drives him to admit the truth. Yet, this time, Aunt Polly is doubtful and refuses to believe him until she discovers the piece of bark in his jacket pocket with the note to her that he had claimed to have written.

Tom's moral integrity urges him to reveal the truth when he decides to help Muff Potter. Unable to stand by while Potter is wrongfully accused of Dr. Robinson's murder, Tom chooses to testify at Potter's trial, despite the risk this decision poses due to Injun Joe. Although lying comes naturally to him, Tom's moral sense and readiness to speak the truth when it matters create a stark contrast with Injun Joe. Injun Joe, lacking a conscience and prone to malevolence, lies and deceives others for his self-interest.