To make some distinctions,
hip hop is the art form and the
music that originated mostly in the
Bronx in the seventies. It was invented exclusively by
black people, most of which lived in the all-black
projects. Hip hop traces its roots to block parties where
DJ's would spin
records and find the "breakdowns" of the drums, and then loop that over and over to make dance beats. Eventually, DJ's began to
rhyme quickly over the
break beats to introduce songs and from there is where we have modern hip hop.
Rap, however, is a derivative of hip hop. There are a number of differences. Hip hop music tends to celebrate life and self knowledge and to expose and express the frustration of oppressed people in this country, while rap music tends to celebrate it and exaggerate it. This isn't because black people like "totin' gats" or "beatin' bitches". It's because when white people originally heard hip hop, to them it sounded like angry, scary black people. That's how white people understood it. When we look at the record industry today, we see that the money and thus the power isn't held by the rappers or even the Puff Daddy's and Jay-Z's and Suge Nights. They have money, but are really pretty low on the food chain when one considers the people who own the major labels. What we have with rap music is a case of white people commodifying the expression of black people in exchange for money. The actual message and purpose of hip hop has been removed from that, and as a result, you get the same type of generic crap that you could expect from the Backstreet Boys or any commercialized crap, just in a different context. Although, to the credit of rappers, the content of their rhymes may be a sham, but the real goal is to make rhymes that are more clever, which they do enough to make me listen.
Basically, hip hop is the music we are talking about. In rap music, almost all of the beats are recycled, most artists do not write their own lyrics, the artists that do write their own lyrics usually bite a style or a few lines from someone else, all the claims made are completely false (I have the pre-release Philly's Most Wanted album -- these guys haven't even dropped an LP yet and they talk about Bentleys), and it is in general counterproductive to the purpose of black expression.
Go listen to The Message by Grandmaster Flash and the Furious Five. I'm sure most of you have heard it, or at least the beat being ripped off by Puff Diddy or whatever, but give the lyrics a listen. It's not a song for bumping in your car, it's a freaking 8 minute long gripe about living in the damn hood. That, my friends, is hip hop.
Note: a lot of people have objected to the way i have phrased things here and I feel the need to clear up a few things. This was a very casual writeup, not intended in any way to be a source of factual information. It was really more of a rant than anything else, but the things I said are still true. When people complain, they usually point out that hip hop is technically the culture that surrounds rap but is much greater than it. I agree completely. When i used the word (words? is it one or two?) hip hop here, I was simply referring to the rap music that is a part of the culture. Hip hop culture has nothing to do with selling crack or using women or driving BMW's. Or rims. Or "ice" or crystal or whatever. My point was that, in this day and age, in the arena of rap music, one can pretty easily draw a line between those who's music is a part of the culture and those who's music is a perversion of the art form. Now I may not be "technically" right, but anyone who is an avid listener of rap music will know the divide that i'm talking about. There is not much of a middle ground (this is arguable, but I'm talking about rap thats coming out NOW). So, when I misuse these terms, I do it because that is the easiest way I can make the layman understand that the rap music he hears on the radio and hears Sen. Lieberman trying to attack may not be representative of the art form in general.
Also, people have raised concerns with my statement that hip-hop is an exclusively black (and latino) art form. I'd argue that they are simply wrong.. the music and culture has very specific roots and they are all among blacks and latinos. I'm sorry asians and whites, but you were not around during the birth of hip hop (I'm white, so BACK UP).