1. Basically, Jazz is music derived from a mix of of afro-american blues and western classical music, but it has evolved into a very different beast. If you want to listen to some of the ways jazz has changed, listen to some Louis armstrong (preferably with Ella Fitzgerald), then some early Miles Davis, Charlie Parker, Dizzy Gillespie, then some John Coltrane (Giant Steps), Later Miles (Bitches Brew), Kenny Barron, Keith Jarret. YOu can see that Jazz changes and can be quite hard to define.
What makes jazz different I believe is the way Jazz is a blend between bluesy, "soul" and classical intellect. Good Jazz appeals to the head, the heart, and the groin, not always in that order. Musically, one of the things taht characterises most jazz is improvisation. Improv in jazz is a lot different from most blues or rock solos, in which a soloist will use one scale over a set key. In jazz, soloists will usually improvise over each chord that is played, using scales from all different keys.
Common scales used in jazz are the mjor scale and its modes, the melodic minor scale and its modes, the diminished scale, and the whole-tone scale.
Roughly, to improvise in jazz, a soloist will look at the chord changes and work out what scales sound good over each chord, and see how to navigate melodic lines through the different scales. Of course, a good jazz player doesn't have to keep working out goood scales, he or she can automatically see what scales will work, and play notes from those scales. The more advanced they are, the more they can simply play any note they want, as long as it sounds good, but getting to the stage where you can simply pick notes is very, very difficult.
"Dozens of people spontaneously combust each year, it's just not that widely reported".
