When the author tries to convince you of his or her opinion, or tries to convince you to buy something. Example : The Coca Cola Ad
When the author presents information to you. Example: During the course of 1999, the writers and editors of Newsweek undertook a massive effort called “Voices of the Century” to chronicle the history of the 20th Century by seeking out and interviewing the men and women who themselves made history. The result was thousands of hours of interviews with everyone from the average front-line Joe in World War II to sports superstars and entertainment legends, distilled into three special issues that were published over the course of the year. Now the staff of Newsweek.com has produced this multimedia version of “Voices”: tribute to the 20th Century.
When the author's intent is mainly to entertain the reader. Example: CLIFFORD'S FIRST SCHOOL DAY Clifford's first day at school is filled with finger-painting, cookie- baking, and other messy misadventures that make Clifford more lovable than ever!