The next step in using Major scales is to take what we learned about the harmonized Major scale and apply that to improvising over an actual chord progression. To do that, you need to locate the key centers within the chord progression, using your knowledge of the harmonized Major scale.
First, we will take a simple progression to illustrate this process and then a more complicated one to demonstrate how to recognize key changes. For our simple progression we will use:
| Cmaj7 | Am7 | Dm7 | G7 |
First start with Cmaj7. As we learned last time, the major seventh chord occurs on the I and IV in the Major scale. This means that at this point we could be in the key of C, (I chord), or the key of G, (IV chord). Next move on to the Am7, which could be key of G, (II chord), F, (III chord), or C, (VI Chord). So far we have two common keys C and G. For Dm7 we have the key of C, (II chord), Bb, (III chord) and F, (VI Chord). Now we have one common thread, the key of C. When you look at the G7 chord, this is the V chord in the key of C, so now we have located our key center for this progression, and can use the C Major scale to improvise over it.
This becomes more complicated in most progressions, as a song will rarely stay in the same key. Using a slightly more complicated progression, let’s see how this works. This time we will use the progression:
| Gmaj7 | Am7 | Bm7 | E7 | Am7 | D7 | Gmaj7 |
Taking the same approach that we did before Gmaj7 could be the key of G, or D, Am7 the key of G, F, or C, Bm7 the key of A, G, or, D, E7 the key of A, and D7, the key of G. The first two bars then are in the key of G, but what about the third? As a rule, when in doubt treat a minor seventh as a II chord, which puts bars three and four in the key of A. The last two bars then go back to G.
Keep in mind that this is just a starting point, and that there are other ways to analyze a chord progression, but this is a good way to get started using your major scales over progressions. This is also assuming that there are only major key centers in the piece you are working on which often is not the case.
The best way to get this all going is to try and find as many progressions as you can to apply this to. The more you do it, the easier it will get. Eventually, you will be able to recognize the key centers without going through all of this analysis. Learn to recognize common progressions, (II, V, I for example), and this will allow you to concentrate playing rather than thinking, progressing toward your goal of playing what you hear.