TaintedYouth wrote:OOOOOOO. So yuri would be sex and a relationship plot. Makes sense now.
Look at it this way. When you talk about a genre of males in love with each other (emotions - shonen ai), you can't mention anything physical unless you classify it as yaoi (sex = physical attraction). So the two go hand in hand when talking about romantic *and* physical relationships. If you just talk about shonen ai - then you're just talking about emotions. But you can't assume that yaoi is sex alone - it can include emotions as well, making it both yaoi *and* shonen ai.
Shonen ai = romantic love
Yaoi = physical love which may or may not include romantic love
Imagine Het (hetero, hetorosexual - the male/female pairings) anime. The classifications are:
Romance = romantic love which may or may not include physical attraction
Hentai = gratuitous sex
You can have Romance without including hentai with het pairings because that's the way the genre is set up. But with yaoi or yuri - to make the names even better at warning away homophobes, you do things backwards. You have Shonen ai instead of Romance - but excluding anything physical. For the anime with both emotions and physical attraction, it falls under yaoi with an inclusion of shonen ai.
I don't know how else to explain it....You can't call an anime where two people kiss shonen or shoujo ai because kissing is linked to physical attraction which is in turn linked to sex. Those anime have to be yaoi, yuri, or het - physical as well as emotional.