In the “Explanatory” to his novel The Adventures of Huckleberry Finn, author Mark Twain writes:
In this book a number of dialects are used, to wit: the Missouri negro dialect; the extremest form of the backwoods Southwestern dialect; the ordinary “Pike County” dialect; and four modified varieties of this last. 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.
Huckleberry Finn is one of the first American novels to be written using vernacular speech, which is the informal language of everyday conversation in a particular country or region of a county. The vernacular speech of a particular area of a country—such as areas of the State of Missouri in which Huckleberry Finn is set—consist of a number of dialects, or variations of vernacular speech, like the dialects that Mark Twain takes great pains to represent in Huckleberry Finn.
Because dialects are informal, everyday speech, characters in Huckleberry Finn speak as themselves, as they truly are, without affectation, except for those who clearly attempt to present themselves above their station, such as the Duke of Bridgewater and the Dauphin of France, who nevertheless reveal their origins through their underlying dialect.
In this way, the dialect in which a character speaks reveals their societal status, as well as their level of education and their occupation, and can also reveal where the character has spent any considerable amount of time during their life.
Huck speaks in “the ordinary ‘Pike County’ dialect” because Pike County is where Huck lives, and that’s where he grew up. Tom Sawyer in Twain’s The Adventures of Tom Sawyer speaks the same dialect as Huck does, but on a slightly higher education level, and although Tom’s Aunt Polly speaks the same basic “Pike County” dialect, her far more grammatically correct speech reflects a higher level of education than Huck or Tom ever had.
The “Missouri negro dialect” is used by Jim, a runaway slave, and by other slave characters throughout the novel. At first, Jim seems to be a wholly uneducated, simple-minded, superstitious, and passive character. As the novel moves forward, and Huck and Jim move down the Mississippi River, Jim is revealed as a careful observer of the natural world who is understandably cautious of the man-made world around him:
Some young birds come along, flying a yard or two at a time and lighting. Jim said it was a sign it was going to rain. He said it was a sign when young chickens flew that way, and so he reckoned it was the same way when young birds done it. (Chap. VIII)
Chickens knows when it’s gwyne to rain, en so do de birds, chile. (Chap. IX)
When Jim believes that he’s going to be set free from slavery, he shows his depth of feeling, gratitude, friendship, and loyalty to Huck for interceding on his behalf and preserving his freedom:
Pooty soon I’ll be a-shout’n’ for joy, en I’ll say, it’s all on accounts o’ Huck; I’s a free man, en I couldn’t ever ben free ef it hadn’ ben for Huck; Huck done it. Jim won’t ever forgit you, Huck; you’s de bes’ fren’ Jim’s ever had; en you’s de only fren’ ole Jim’s got now. (Chap. XVI)