One of the linguistic features Twain uses thematically is dialect. He uses a different dialect for each group.
In the “Explanatory” to the book, Twain explains that he is writing the way people talk. Twain explains that he did not just make them up, and the characters are not trying to talk alike.
The shadings have not been done in a haphazard fashion, or by guesswork; but painstakingly, and with the trustworthy guidance and support of personal familiarity with these several forms of speech. (p. 5)
Although the “Explanatory” is humorous, Twain is drawing attention to the dialects from the beginning. By using realistic speech, he reinforces the theme that it is important to acknowledge differences in people. Not everyone is alike. He also acknowledges the importance of class, another significant theme in the book. Huck comes in contact with several different classes, including slaves and conmen. He learns that the people who are supposedly upper class do not really have morals, whereas the lowest class, slaves, often do.
Throughout the book, Huck tries to reconcile his society’s expectations and beliefs about slavery with his experiences with Jim. Jim is a good man, whereas many of the white men were not. Huck realizes first that Jim has feelings, and second that he cares about his family as much as a white person.
He was thinking about his wife and his children, away up yonder … and I do believe he cared just as much for his people as white folks does for their'n. (ch 23, p. 102)
An example of white values is demonstrated when Huck describes how his boat ran aground, and Aunt Sally (Tom Sawyer’s aunt) asks if anyone was hurt, we learn that she doesn’t consider slaves human.
“Good gracious! anybody hurt?”
“No'm. Killed a nigger.”
“Well, it's lucky; because sometimes people do get hurt…. (ch 32, p. 146)
Twain emphasizes linguistic differences between people, and that reinforces the difference in values. The people who are supposed to be good are not what we would consider good, and the slaves, who are supposed to be subhuman, are often good people.