As I've mentioned, most tunes (especially jazz tunes) have a lot of ii-V-I progressions that require you to play in more than one key during the same tune. This next tune, "Hey Dude, Where's My ii-V-I?", has 3 different ii-V-I progressions. You know two of them, ii-V-I progressions in Bb and Eb concert, can you find the third one, and figure out what key it is in? Remember to find the Major chord and work backwards. The I chord will give you the key you should be playing in for the whole progression. Here we go, find the ii-V-I's.
Find it? Yes, the last line is a ii-V-I in the key of G Major.. so to play this tune, you have 8 bars in Bb, 4 bars in Eb and the last 4 bars in G. Now I'll help you out by color coding the progression so you can see exactly what is happening with the chord changes. Playing in Bb is blue, in Eb is red, in G is in green. Pretty cool, huh?
So now that your eyes have been dazzled by color coding, I'm going to eliminate it, since most music you play in the real life jazz world won't have nice colors. What there will be is a melody to play, and then a series of chord changes, with guide tones also. We've talked about what chords to play, so... 1, 2, you know what to do!
And there you have it! We will go further with how to make changes later, but these are the basic techniques that you will always use. Find what key you are in, find the other keys the tune temporarily goes to, find the scales to fit, then play roots and then the guide tones (3rd and 7ths). You can do this for any set of changes. One other item of interest is how closely keys are related. Remember that a relative minor key is VERY closely related, as they have the exact same key signature. Like a parent and child. When you are playing this chord progression, the keys of Bb and Eb (concert) are closely related, but not quite as close as a relative major or minor. But they are only one key away, the difference between two flats and three flats. They are like nephews. The next key is a bit further apart. The key of Eb has 3 flats, the key of G has one sharp. This is a difference of 4 flats or sharps (or combination). So that last key of G is a bit more of a shock, and also slightly more difficult to navigate, since it's not related as closely. Consider it your 2nd cousin.
More about this later, but for now will will delve into the roots of all jazz, the blues!