Wheat's BassBook: A Comprehensive Method & Resource for the Electric Bass Guitar

Playing Diatonically

I've presented you with each of the scales we've covered and with the primer on chords because I'd like to show you how to play diatonically before we move on to scale substitutions and progressions with non-diatonic chords. Diatonic means "of the scale." Earlier, we built a CMaj7 chord by taking every other note of the C scale, begining with the root (C). Thus, our formula for a CMaj7 chord is the R, 3, 5, 7 of the C Major scale. We can also build chords off every other note in a scale, and due to the intervalic construction of the C Major scale, we will get certain sorts of chords on each interval.
This can be very confusing, and I'd like to make it very clear, so lets take a look at the C major scale again:
C   D   E   F   G   A   B   C   (note names)
R   2   3   4   5   6   7   R   (note interval names)
  W   W  1/2  W   W   W  1/2    (intervalic construction)
The notes of the C major scale are not equally spaced. Some notes are a whole step apart (indicated with the W, above) and some are only a half-step apart (indicated with a 1/2, above). Take a look at a C major scale played on only one string of your bass and this pattern of whole and half steps will become clear:
          3       5       7   8      10      12      14  15
You'll notice that there is a whole step between most notes, but there is only a half-step between two pairs of notes (E & F; B & C). This pattern of whole and half steps is what gives the major scale it's characteristic sound. But there are lots of other sounds lurking in the C major scale. If you build a scale off of each note of the C major scale, you get the modes we discussed earlier:
            B C D E F G A B  (locrian)
          A B C D E F G A  (aeolian)
        G A B C D E F G  (mixolydian)
      F G A B C D E F  (lydian)
    E F G A B C D E  (phrygian)
  D E F G A B C D  (dorian)
C D E F G A B C  (ionian)
If you build seventh chords off of each of those modes (using the every other note method), you get something like this:
                        (B)  C  (D)  E  (F)  G  (A)  B    (locrian)
                    (A)  B  (C)  D  (E)  F  (G)  A    (aeolian)
                (G)  A  (B)  C  (D)  E  (F)  G    (mixolydian)
            (F)  G  (A)  B  (C)  D  (E)  F    (lydian)
        (E)  F  (G)  A  (B)  C  (D)  E    (phrygian)
    (D)  E  (F)  G  (A)  B  (C)  D    (dorian)
(C)  D  (E)  F  (G)  A  (B)  C    (ionian)
Extract those chord tones (the ones in parethesis above) and you get this sequence, which we number with roman numberals, starting with Cmaj7:
Chord Tones  Mode         7 Chord   Tritone   Degree

B, D, F, A   (locrian)    Bm7b5     Bdim      vii
A, C, E, G   (aeolian)    Am7       Am        vi
G, B, D, F   (mixolydian) G7        G         V
F, A, C, E   (lydian)     Fmaj7     F         IV
E, G, B, D   (phrygian)   Em7       Em        iii  
D, F, A, C   (dorian)     Dm7       Dm        ii
C, E, G, B   (ionian)     Cmaj7     C         I

This is sometimes called the "harmonization of the major scale." You can harmonize any scale and you can harmonize this one in different ways, but this is any easy example that will help you understand music theory. Some people like to use upper-case roman numerals for the major and dominant chords while using lower-case roman numerals for minor and half-diminished chords. When someone says they're playing the "one" chord in the key of C, they're refering to C or Cmaj7 (depending upon the musical context). The "two" chord would be Dm(7). The "three" would be Em(7). I'm sure you get the idea.
It's best if you can hear these chords played on the piano or on a guitar, but in case that's not an option, I've notated them here for the bass (using 7th chords and omitting the 5th degree in most cases):
 I   ii iii IV   V7   vi  vii7b5
Using E-string roots, you could play it this way:
 I   ii   iii  IV    V   vi   vii
What to Play over a Given Progression
There are many interesting theories about which scale fits over which chord. But just sticking with what we've already covered here, we can play some very musical melodies over these chords. Suppose you are playing (or writing) a song which contains the following progression (one bar per chord, ad nauseum):
C    F     Em     G
I    IV    iii    V
You can approach a progression like this at least two different ways. You could just look at the chords and play a major scale (Ionian mode) over all the major chords and a minor scale (Aeolian mode) over the Em. In that case, you'd think of the progression like this:
C     F     Em      G     (chord in progression)
I     IV    iii     V     (degree of chord)
Cmaj  Fmaj  Eminor  Gmaj  (scale)
Another way to approach the progression (and IMHO a more melodic way) is to use the modes we learned above and play a different mode for each chord:
C         F         Em         G             (chord in progression)
I         IV        iii        V             (degree of chord)
C Ionian  F Lydian  E Phygian  G Mixolydian  (scale)
Note that some things remain the same with either approach. We still played a C major scale over the C (a.k.a. the "I" chord or the "one" chord), but for each of the other chords, we used a different mode. Each approach has its advantages, and you will probably use both. When I don't have time to analyze a progression fully, I use the first approach (we might call it the major/minor approach). When I have more time to think about the chords, or when I need a more melodic line, I use the modal approach.
At this point, you might say to yourself, if all of the modes come from the major scale, then I'm not really switching scales at all when I play over these chords; I'm just playing C major and starting on different notes. On one level, of course, you'd be right. A minor is, after all, just C major starting on the sixth degree, but the sound changes dramatically. To my ears the modal approach is more melodic, but to some people it is sickeningly melodic, and it doesn't work all that well over chord progressions which contain (or are mainly composed of) non-diatonic chords. This brings us to the next topic.
What to Play over Non-Diatonic Chords
Most of the songs that I write or play over are built out of diatonic progressions, so I'm no expert on non-diatonic playing (though I'm working on it). Therefore, you should take what I have to say with a grain of salt. Jazz players are the most adept with non-diatonic progressions, since jazz composers are very fond of these. Still, I can offer a few pointers and you can ask the friendly people on the bass newsgroups if you need more specific advice.
1. The easy way to tackle a non-diatonic progression is to use an expanded version of the major/minor approach we learned earlier when working with diatonic progressons. It can be summarized as follows:
2. If the progression looks mostly diatonic, but with an odd non-diatonic chord thrown in between two diatonic chords, try using the same mode that you would use on the chord directly preceding the non-diatonic chord, or the one directly after it. That is, use the same pattern, but position the pattern so that it starts on the root of the non-diatonic chord.
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