When is it influenced and when is it stealing?

[KMommy]

This actually came up at work concerning music but then I read the Mencia post here. When do you consider someone's work stealing? There is an episode of The Bernie Mac show where Chris Rock is a guest star. Bernie is mad at Chris because he has been stealing his material. In the show Chris is flat out taking Bernie’s material almost word for word. At the end of the show they are sitting in the Limo and Chris tells Bernie that he has always looked up to him and that he wanted to be like him so of course there will be times when he sounds like him. Then he said "You know like sometimes your going to sound like Redd or Richard..."

So when is it stealing? When it is almost word for word or just when it is the same type or style and the comic/artist doesn't give the originator the credit for his influence?
What do you all think?

[mojones]

KMommy,

Ahhhh a good question. My opinion shifts on this all the time. But generally, I consider it stealing when it's word for word. Or almost word for word. Most comedians will use other jokes as a template for their own tags. That's how we learn to structure a joke. But I don't think that qualifies as stealing because you're using the form -- not the substance of a bit. To use the same tag and structure is just outright theft!