In creating bass lines using pentatonic scale, do you use the pentatonic scale of the key you are in or of the chord you are playing?
ROLE: Bass player
PRIMARY OBJECTIVE: Support the RHYTHM and the HARMONY of the SONG.
Q: Do I use the pentatonic scale of the key or the chord?
A: Whatever you do, do not jeopardize the PRIMARY OBJECTIVE of your mission.
Let's compare the use of pentatonic scales for guitarists vs bass players.
Why do guitarists use pentatonic scales?
Guitarists use (major and minor) pentatonic scales in guitar solos mainly for the following reasons:
- Reason 1: beginner safety. Playing pentatonics "of the key" is a safe shortcut to soloing not-blatantly-wrong notes without knowing what you're doing and what's happening with chord changes. The major and minor pentatonic scales are harmonically slightly ambiguous, because they lack the two harmonically strong and polarizing notes (out of the seven diatonic notes), and so it's more likely that a randomly selected note will not sound horribly wrong. Randomly played pentatonic scale notes sound like staying relatively close to "home" position.
- Reason 2: bluesiness. The pentatonic scales can sound bluesy, even without using so-called blue notes.
- Reason 3: outside playing. In jazz style solos, pentatonic scales can be used for their "home position" characteristics - not to enforce the original home key but to bring flavors form other keys. One way to bring an "outside" playing feeling it to use pentatonic scales from different keys. As an example that's often used in blues/soul styles is to play pentatonics from the key three semitones higher. For example in C major, you would layer C minor (Eb major) pentatonics, creating a bluesy modal mixing sound.
Why would a bass player use pentatonic scales?
Why would a bass player use pentatonic scales, when not playing a bass solo??? When playing accompaniment, they're not supposed to be doing basically any of the stuff that guitarists try to do in their solos.
A single bass note can have a relatively large impact on the total harmony of the band, compared to any single note that a guitarist might play in a solo. Particularly in the rhythmically strong beats of the comping pattern (whatever the meter and pattern might be), the bass player can change the whole overall chord to something completely different by playing one single note. If the rest of the band plays an F chord and the bass player plays a G, the overall chord just became essentially a dominant chord heading to C. But if the bassist plays a D, the overall chord became a Dm7.
If you play pentatonic bass lines that do not highlight the chord tones on the strong beats of your rhythm pattern, then you're not supporting the written chords. It may still sound good, you're just changing the whole chord progression to something else.
However, the bluesy-sound reason for using pentatonics might apply for in-between filling or passing notes, as long as your strong-beat notes support the harmony.
There are many styles of writing bass lines, but they all have one thing in common: the bass line has to support the intended harmony progression. Pentatonic scales only have five notes, so one pentatonic scale per key only covers a small part of the potential chords you might have to support. The other way, pentatonic scale per chord, isn't much better either. As an easy example, if you're supposed to support a diminished seventh chord - trying to overlay a minor or major pentatonic scale with the chord's root note is going to spoil the chord.
To sum this up, I'd simplify all this into: at least in the beginning of your bass player journey, forget about pentatonic scales. It's much more important to know and to practice the basic diatonic seven-note scale of the key and to know all chord tones. After you can play chord tones, you can start adding some walking or approach notes in your bass lines from the basic diatonic scale of the key, or even chromatic approach notes. Or play alternating bass, i.e. alternate between the root and its fifth, like C and G for a C major or C minor chord. This is bread-and-butter stuff for bass players.
If you feel that you absolutely must overlay pentatonics (of the key, or rooted on the chord's root) on a chord, you still have to know all of the intended chord's chord tones, to understand if and how the pentatonic notes might fit in there. The total end-result will be non-pentatonic anyway.
Pentatonic scales are fun to play and very commonly used for improvising and also creating melodies and lines for all instruments including bass.
When you say bass lines I assume you are talking about lines that make up the bass part of a song and not just playing lines from the perspective of improvising and soloing. If you are thinking of soloing then it is fairly typical to play a single pentatonic scale over a chord progression since you are not concerned with playing a stable supporting bass line at that point.
If you are thinking of creating a bass part a different approach is required. First of all there are not enough notes in the pentatonic scale to cover the roots of the seven diatonic chords that exist in a major or minor key, not to mention non-diatonic chords. For example if you were in the key of C and had to play an F chord you would be out of luck with a C pentatonic scale. Another issue is bass lines are the harmonic foundation and rely heavily on chord tones, especially thirds and fifths. Once again a single pentatonic will leave you high and dry. For this reason a single pentatonic scale does not work for creating a bass line over a progression
If you want to use pentatonic scales for creating bass lines the best approach is to use the major or minor pentatonic scale that goes with whatever chord you are playing at that moment. Both major and minor pentatonic scales have the root, third and fifth plus two other useful notes. This will allow you to create coherent motif based baselines over chord changes. It is not foolproof, you have to examine the context and use your ears to see if it works in different situations but you can do quite a bit with this approach.
I would also like to point out that using pentatonic scales to create bass lines is only one of many different approaches you can take and is not really the best approach to creating good bass lines.
This very question was asked by a student in one of my lessons last week.(A guitarist becoming bassist).
First to establish is which pentatonic scale we're talking about. There are two - major and minor.
The minor pent. doesn't work well, as there are notes which clash with the underlying chord - mainly the 3rd. In pent. min., it's ♭3 which doesn't blend well with the M3 in the chord itself. That m3 works fine when used for soloing in Blues - although it often gets that stretch up to (or near) the M3 anyway, but doesn't have the same effect when played on bass.
The major pent. does work well, as it contains all three notes that occur in the underlying chord - 1, 3 and 5. And the main job of a bassist - in the majority of pieces - is to outline the chord played.
Having said all that, and pointed out the differences between maj. and min. pents., it will be, as often the case, genre specific. Thus, the ♭7 from min. pent. will fit when the chord changes from I to IV, say, and the M6 from maj. pent. will work when I is followed by another I.
Consider also, as most seasoned players do, of mixing the two! Think of the bassline 1 3 5 6 ♭7 6 5 3 , over two bars - quite a well known pattern that blends the two!
EDIT: to more specifically answer the question(s), only using the notes of the pentatonic scale from the key won't work particularly well. Changing to use the pent. notes from the current chord will work beetter - but bear in mind what I've said earlier.
You could use a five tone pattern and move it over a chord progression, something like this...
But, you should also consider that can be viewed as just some passing tones between a simple arpeggiation of the chords, like this...
Also, when you consider all the tones that are used after moving the five tone pattern over the
I IV V chords, you end up playing all the tones of the major scale...
In that example, I think it's questionable to call those "pentatonic" when the end result is not at all pentatonic. The resemblance of the five tone pattern to a pentatonic scale is more coincidence. IMO pentatonic ought to be used to describe music, at least melodies, that are truly limited to just a five note scale, and that is not the same as isolated measures of five tones.
...do you use the pentatonic scale of the key you are in...
Of course you can do anything you want, but the typical role of the bass is to establish the harmonic foundation. Usually the bass works around chord roots or chord tones. If you used only a pentatonic scale in the bass, while playing some progression like
I IV V7/V V, you will potentially have places where the bass isn't matching the chords, or certain chord roots are not available in the pentatonic scale. FWIW, you can get a pentatonic scale to match some chord tones even in a progression with lots of secondary chords, but doing that in the bass means playing a lot of inverted harmony instead of chord roots. That may or may not work for all kinds of different reasons.
Two theory terms that come to mind are ostinato and pedal point both of which can occur in the bass. Look up those terms. The basic idea is the bass would repeat a pattern or hold a tone while the other instruments play chord changes. The separate parts often start together, move apart from each other harmonically and create dissonance, then return to match each other. This is one way you might get a pentatonic pattern in the bass to work with chord progressions that "don't fit" the pentatonic scale.