Bebop Scales

The basic idea behind Bebop scales is simple. But looking at five different sources, I found inconsistent terminology and contradicting definitions. This post intends to sort things out in the world of Bebop scales.

Traditional Bebop Scales

By inserting an additional chromatic passing tone into ordinary diatonic scales it is possible to play endless lines of eighth notes in stepwise motion where chord-tones always fall on strong beats, non-chord tones on off beats. This makes for strong melodic lines that clearly state the underlying harmony.

Despite this simple idea, the topic is confusing. Different authors use conflicting terminology. Often referring to the same scale by different names. In one case referring to different scales by the same name.

Then there is the “Major 7th Chord Dilemma”. Alternating chord-tones and non-chord-tones are only obtained when the chromatic passing tone is inserted between the 7th and the Root of the underlying chord. This is only possible for chords with minor sevenths. There is no space between a major 7th and the Root. The “solution” is to use the Major Bebop Scale with the passing tone between the 5th and 6th of the chord (see scale below). Why does this work?

I believe that there is a simple way of deriving all the scales commonly referred to as Bebop scales in a simple but theoretically sound way. This derivation also produces scales with the desirable strong harmonic connection that are not mentioned elsewhere.

I looked at the following five sources to get an overview of the various Bebop scales in common use:

The following is a summary of the different scales found in the literature. The notes are color coded: Black notes are chord tones of the underlying harmony, the red note is the chromatic passing tone and blue notes are non-chord tones from the underlying scale.

Major Bebop Scale

Riposo, Halberstadt, and Wikipedia refer to this scale as Major Bebop. Baker, the Scale Syllabus and Wikipedia call it Bebop Major. As mentioned above (Major Seventh Chord Dilemma), there is no Bebop Scale that directly matches a CΔ7 chord. That’s why it’s shown here as outlining the harmony of a C6, the major-sixth chord.

Mixolydian Bebop Scale

Halberstadt calls this one Dominant Bebop. Other names are Bebop Dominant (Baker, the Scale Syllabus, Wikipedia),  Mixolydian Bebop (Riposo) and Mixionian (Wikipedia).

Minor Bebop Scale

Also known as: Dorian Bebop (Riposo), Bebop Minor (Scale Syllabus), and Mixodorian (Wikipedia). This scale is intended to be played over ii-Minor chords in ii-V-I progressions. As can be seen in the note example above, the scale does not alternate the chord-tones from D-7, as one would expect. A close look reveals that this scale is really not a distinct scale but the fifth mode of the Mixolydian Bebop Scale mentioned above (i.e. Mixolydian Bebop Scale starting on its fifth).

Dorian Bebop Scale

Only the Wikipedia article talks about this scale and refers to it as Bebop Dorian Scale or Dorian Melodic Bebop Scale. This scale follows the basic principle of inserting the chromatic passing tone between the 7th (minor) and Root of the underlying chord. Therefore it has the property of perfectly alternating chord tones and non-chord tones.

Aeolian Bebop Scale

This scale perfectly outlines the harmony of a minor vi chord, e.g. A-7 in C-Major. Halberstadt calls this one Minor Bebop, Wikipedia calls Harmonic Minor Bebop.

I find both names misleading, as in the Jazz context, Minor most often refers to Dorian Minor. The reference to Harmonic Minor sees justified, since the traditional Harmonic Minor scale is contained in the Aeolian Bebop scale. I’d like to point out though, that the raised 7th in Harmonic minor is a centrally important note, whereas in the Aeolian Bebop it is merely the chromatic passing tone, which would never receive emphasis, if the scale is applied as intended.

In my opinion, the importance of the Aeolean Bebop Scale stems less from its applicability to minor harmony, but the fact that the Major Bebop Scale is indeed a mode of Aeolean Bebop. E.g. A-Aeolean Bebop played from its third note is indeed the C-Major-Bebop Scale (see above).

Half-Diminished Bebop Scale

Riposo introduces this scale as the Half-Diminished Bebop Scale. Wikipedia calls it Phrygiolocrian. Aebersold’s Scale Syllabus simply refers to it as Bebop Scale. This is probably due to the fact that we have seen this scale before in form of the Mixolydian Bebop Scale. Half-Diminished Bebop is the third mode of the Mixolydian Bebop Scale. Because of this, the scale doesn’t strongly outline the harmony of the underlying half-diminished chord.

Chord Substitution

Of the six scales mentioned above only three have the passing tone between the 7th and Root of their respective chord (Mixolydian Bebop, Dorian Bebop and Aeolean Bebop). The remaining three scales (Major Bebop, Minor Bebop and Half-Diminished Bebop) are modes of those first three. Reharmonization or the practice of chord substitutions offers a straight forward explanation why modes of the first three scales can be used over the Major, Minor and Half-Diminished chords, effectively producing the second set of scales.

Chord substitution happens all the time in Jazz: To create or reduce harmonic motion, to create a fresh sound for an established standard, to open up new melodic choices for the soloist. There are several benefits to using chord substitution in explaining the various Bebop scales:

  1. Every Jazz musician is inevitably being exposed to chord substitution and does (or at least should) have some understanding of it.
  2. Chord substitution is applicable in many more situations than just comping. A soloist can use chord substitution to improvise based on substituted harmony, while the rhythm section stays on the original harmony.
  3. Chord substitution is well understood and there are good books on the topic. E.g. Randy Felts: “Reharmonization Techniques”, Berklee Press, 2002.
  4. In the specific case of Bebop Scales, chord substitution not only explains the how the commonly used Bebop scales work, but enables the creation of other scales with the desirable Bebop-scale quality of clearly outlining harmony.
    In situation where multiple Bebop scales can be used, an understanding of the underlying chord substitutions helps making an informed choice.

For our purposes, we only need some basic chord substitution rules, which are explained in the next section.

Simple Substitution

Simple substitution is the practice of replacing a chord with an other chord from the same harmonic family (Tonic, Subdominant, Dominant Chords). The following shows all 7 diatonic 7th chord in C-Major grouped by family.

What this means in practice is, that playing an A-7 chord while a lead sheet asks for CΔ7 is likely going to be OK. In particular this means that an improviser can pretend CΔ7 has been substituted with an A-7 and make melodic choices based on A-7 rather than CΔ7. This second technique can help produce much more hip sounds than when locking closely to the requested chord. It is also the trick we’ll use to apply Bebop scales over chords other than the ones they were derived from.

Extended ii-V-Patterns

Extended ii-V-Patterns refers to the practice of replacing an extended period of a V7 chord by a ii-V-Progression. E.g. replacing one bar of | G7 | with | D-7  G7 |. This rule can also be applied in reverse, i.e.simplifying a  ii-V-progressions, replacing it with just the V-Chord.

Bebop Scales and Chord Substitution

We’re now going to apply the following two rules to Bebop scales.

  • Rule 1: Any chord can be replaced with another chord from the same family.
  • Rule 2: ii-V-Progressions can be simplified to just the V-Chord.

Solving the Major 7th Chord Dilemma

Let’s first resolve the Major 7th Chord Dilemma. Let’s assume a C-Major tune calls for a CΔ7 chord. We know there is no scale we with an extra note between the 7 and the root.

Instead we pretend CΔ7 was substituted with A-7 (according to rule 1). The matching mode of the C-Major scale for an A-7 chord is Aeolean. “Bebopification” (i.e. inserting a chromatic passing tone between the 7th and root) of Aeolean give us the Aeolean Bebop scale.

The third mode of Aeolean Bebop (playing it starting on its third note) is indeed the same scale as the Major Bebop scale. So substituting a IΔ7 with a vi-7 explains why the Major Bebop Scale is indeed the third mode of the Aeolean Bebop Scale.

Explaining the Minor- and Half-Diminished Bebop Modes

Both, the Minor Bebop Scale and the Half-Diminished Bebop Scale, are modes of the Mixolydian Bebop Scale.

Half-Diminished Bebop

We’ll again use Rule 1 to substitute a vii-7b5 chord with a V7 chord. In C-Major this would replace a B-7b5 chord with G7. The matching Bebop Scale for G7 is Mixolydian Bebop. This confirms why the Half-Diminished Bebop Scale is indeed the third mode of the Mixolydian Bebop scale.

Minor Bebop

In order to derive the Minor Bebop scale, we need to apply substitution rule 2: “Extended ii-V-Patterns”. When looking at a ii-V progression, we can simplify the following two bars:

| D-7 | G7 |

to simply two bars of

| G7 | G7 |

effectively substituting the D-7 with a G7. The appropriate Bebop scale for G7 is G Mixolydian Bebop, which explains why some texts define the Minor Bebop Scale to be the fifth mode of Mixolydian Bebop.

Choosing the best Minor Bebop Scale

Now that we have two different scalesfor  minor 7th chords, the question is if one is better suited than the other in a given situation. Obviously one way to answer this is to try out both choices and see what sounds better.

A simple guideline is based on the fact that we used rule 1 to simplify a ii-V progression into a single V chord.  The  Mixolydian Bebop-based Minor Bebop Scale is a good choice when the minor chord in question is part of a ii-V-I progression.

If the minor chord has tonic function Dorian Bebop would be the better choice. Example: In the following minor ii-V-i progression

| B-7b7 | E7alt | A-7 | A-7 |

the A-7 serves as the tonic and thus using A-Dorian Bebop would be the better choice.

Beyond Traditional Bebop Scales

Up until now we have used basic chord substitutions to explain the Bebop scales commonly described in Jazz theory books. We did this by combining chord substitutions and three basic Bebop Scales, namely those with a chromatic passing tone between their 7th note and their root (Dorian Bebop, Mixolydian Bebop and Aeolean Bebop).

Since a major scale consists of 5 whole steps and 2 half steps, there must be two more “basic Bebop” scales we can construct. Using chord substitution rule 1 and those scales will produce Bebop scales that are not found in any of the books I researched.

The following sections explore these “Beyond Bebop Scales”.

Beyond the Major Bebop Scale

When we derived the Major Bebop scale, we pretended to substitute CΔ7 with an A-7t chord. The Tonic family of chords in C-major has yet an other member: E-7 and Rule 1 would also allow us to replace CΔ7 with E-7.

The matching mode of the C-Major scale for an E-7 chord is Phrygian. “Bebopification” of Phrygian produces what I call Phrygian Bebop, a scale that is not mentioned in any of the sources I’ve looked at: When properly applied over a CΔ7 chord, this scale emphasizes the 3, 5, maj7, and 9, effectively producing a CΔ9 sound.

The IVΔ7#11 Sound

A nice chord to end tunes on is a “Major-7th Sharp 11” sound. This is the sound of Lydian scale, the fourth mode of the major scale. Lead sheets often ask for this specific sound via a Δ7#11 chord.

Because of the Major 7th Chord Dilemma it is not possible to bebopify the Lydian scale. In C-Major the F-Lydian scale would be a perfect match for the FΔ7 chord. Using rule 1 we can substitute D-7 for the FΔ7(#11). The appropriate scale for D-7 is Dorian Bebop. As with the IΔ7 this scale would emphasize the Root, 3, 5, and 6 of the chord, effectively producing a Major-6 “Lydian” sound.

The usefulness of this scale in practice is somewhat questionable. The Lydian mode has no avoid notes, so it is more amenable to placing any of its notes on strong beats.

Also, its only difference to (Ionian) major is the #11 and there’s a good chance that emphasizing that note is the right thing to do; which unluckily is not what the scale does.

Beyond the Mixolydian Bebop Scale

Since the Half-Diminished Chord and its matching diatonic mode Locrian have have a minor 7th, it is possible to bebopify the scale to Locrian Bebop, another scale not mentioned in the Bebop Scale literature: This scale perfectly outlines the half-diminished sound and is a good choice for that chord.

Rule 1 tells us by replacing B-7b5 with G7, that the Locrian Bebop scale also works over dominant chords. In the case of a G7 chord, the scale would emphasize the 3, 5, 7, and 9 of the G7 chord, effectively producing a G9 sound.

Summary

By inserting a chromatic passing tone between the (minor) 7th and root, we bebopified five modes of the diatonic major scale: Dorian, Phrygian, Mixolydian, Aeolean and Locrian. The following table lists all five of these Diatonic Bebop Scales.

For each scale all chords compatible with the scale are listed. “Compatible” here means that chord substitution allows for interchanging the compatible chord with the chord naturally matched by the scale.

Applying a Diatonic Bebop Scale to chords other than the natrually matched one is akin to using a “mode” of that Bebop scale. If the particular mode has a commonly used name, it is mentioned under AKA (also known as). Since Bebop scale modes do not outline the four notes of the underlying 7th chord, a chord symbol that more accurately expresses the sound created by the mode is also provided. E.g. the Major Bebop scale for CΔ7 produces a C6 sound.

For reasons of simplicity, the complete table is based on C-Major. The whole system can obviously be transposed to any key.

Fields in orange represent new scales explored in this post and not covered in the literature I looked at. I found the Locrian Bebop on G7 and Phrygian Bebop on CΔ7 to sound great in practice. Both are producing 9th chord sounds.

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2 Responses to Bebop Scales

  1. Marcio Arese says:

    Man, this page together with the Jeff Ellwood’s e-book “Developing bebop lines” were the best things that happened to me, beboply saying. Thank you!

  2. “The basic idea behind Bebop scales is simple. But looking at five different sources, I found…

    …”INCONSISTENT TERMINOLOGY AND CONTRADICTING”…

    …definitions. This post intends to sort things out in the world of Bebop scales.”

    – Frank Jargstorff

    Man, Oh, Man! – You are So RIGHT!

    Thanks for this great blog!

    – Ernie Leblanc, ”Into the Bass!”

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