Not to go off on a tangent but...
In the 80s there was a distinct difference between Hip Hop and R&B.
Actually, when they first started making rap records, they played instruments so Rap records were composed like R&B songs
Rappers Delight - Sugarhill Gang
The Breaks - Kurtis Blow
Freedom - Grandmaster Flash & The Furious 5
Double Dutch Bus - Frankie Smith
It's Magic - Fearless Four
New Rap Language Spoonie G feat The Treacherous Three
Musically, if you listened to the instrumental version of those songs, they sounded like R&B songs. The only difference was the rapping instead of singing. R&B radio stations would play the early Rap records because the songs were composed like R&B and they thought it was just a fad.
First The Message and then Sucker MCs were the first Rap songs that didn't sound like R&B. I mean, when Sucker MCs comes on you know it's not a R&B record. Then Rap producers started using drum machines, synthesizers and scratching became popular. By 1985/86 Rap music (not necessarily Hip Hop, but Rap music) had a distinct sound. The drums were more prominent, the scratching and the vocals sounded unlike anything that had come out prior. Then Rap producers started sampling. Some of the first records that contained samples were;
Ego Trippin - Ultrmagnetic MCs
Eric B Is President - Eric B & Rakim
South Bronx - Boogie Down Production
Make The Music With Your Mouth Biz - Biz Markie
Peter Piper - Run DMC
When those songs came out there was absolutely no way that you could mistake them for R&B records. Rap music had officially become it's own genre of music.
But since the early 90s (I guess it started with Friends by Jody Watley, but you could take it back to P.I.M.P by Rick James or I Feel For You by Chaka Khan) R&B singers started singing over beats that were undeniably Hip Hop beats, like when Mary J Blige rapped over the Top Billin beat for Real Love, or when Jodeci sang over the You're A Customer beat by EPMD (both songs were produced by Puff Daddy).
By the mid-90s Every R&B remix had a rap feature.
By the late 90s/early 00s the instrumental tracks of Hip Hop and R&B became blurred again. At first in the early 80s, Rap producers were biting R&B songs, but in the mid to late 90s R&B producers started biting Hip Hop songs.
Here's 5 songs from the mid 90s.
@Inori are these songs Hip Hop or R&B? Would you say the instrumental track is Hip Hop or R&B? How about the lyrics?
Lastly, if you were visiting another city and the radio station played these 5 songs in a row, how would you describe the radio station?