How immediacy, foreshadowing, and commentary work to show author's purpose, meaning, or tone and style

Many different types of writing exist in the world, ranging from classic Shakespearean plays to politicians' speeches to the screenplay treatments that inspired this summer's biggest blockbuster hits. These works may vary in tone, genre, and type, but as pieces of writing, they should have one thing in common: a purpose.

Authors write for many different reasons. Those reasons are called the author's purpose. Depending on the purpose, authors may choose all different sorts of writing formats, genres and vernacular. A simple trick to summarize the three main categories of author's purpose is to use the acronym PIE, which stands for persuading, inform and entertain. Although there are many reasons to write, to persuade, to inform and to entertain represent the three main forms of author's purpose. Most other reasons can be grouped into those three broader categories. 

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mark twain, real name samuel langhorne clemens, was an american writer, humorist, entrepreneur, publisher, and lecturer. among his novels are the adventures of tom sawyer and its sequel, the adventures of huckleberry finn, the latter often called "the great american novel". wikipedia