Go back and take a look at what some black writers were saying in the 1820s, the 1830s. They make mention of how some white people would tell their children, if you don't behave, we're going to put you in the n - - seat. If you don't behave, we are going to make you sit with the n - - s. That's why we know that, by then, the word had become a slur.

Randall Kennedy