Rap superstars JAY-Z and Nas have spoken out in defence of hip hop in a new book about the music genre. Jay-Z wrote the introduction for Know What I Mean? Reflections On Hip Hop, by Georgetown University professor Michael Eric Dyson - and Nas wrote a passage at the end of the book. The book tackles the use of politics and gender in rap - and the pair were keen to speak out at a time when hip hop is under attack for encouraging violence and promoting misogynist behaviour. Jay-Z writes, "He has shown those doubters and critics that hip hop is a vital arts movement created by young working-class men and women of colour. Yes, our rhymes can contain violence and hatred. Yes, our songs can detail the drug business and our choruses can bounce with lustful intent. However, those things did not spring from inferior imaginations or deficient morals; these things came from our lives. They came from America."