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Understanding a Tune For Improvisation - Introduction
To improvise on the chord progression of a tune, it is necessary to make choices of the specific scales or modes that relate to each chord. Of course, it is important to understand the chord structure and to identify all of the chord tones and altered chord tones. But, to complete the picture, you have to know what choices of scales to make to give the correct or normal sound to the tune! To do this, it is helpful to keep several factors in mind: the chord symbol, the key(s) of the tune, the chord’s function (location of the chord in the key), the melody note(s) in relation to the chord, and the context (preceding and following chords).
Understanding a Tune For Improvisation - The Chord Symbol
Chord symbols may be general (Cmi7, F7, Bbma7) or very specific (Cmi#7, F13b9, Bbma7#11). If the chord symbol has specific indications regarding the sound, it may make the choice of the accompanying scale easy! For example, if you have a major 7th chord and the symbol includes #11, that indicates a Lydian scale which has a #4 (#11) in it. If you have a minor chord with a #7, that requires either a Harmonic Minor or Melodic Minor scale both of which have raised 7ths in them. There may be other factors which determine if one of those would be a better choice but at least it is narrowed down by the chord symbol. If you have a dominant 13th with a b9, that calls for a diminished scale (½ W ½ W ½ W ½ W) because that is the only conventional scale that includes that combination of a natural 13th and a b9. General chord symbols may be more open to personal choice or require other factors to determine the best choice!
Understanding a Tune For Improvisation - What is the key?
If you see two or more chords in the same key, those chords may be “bracketed” with the scale of the key. That means, rather than having a separate scale sound for each chord, the scale of the key will satisfy the sound of all of them! For example, if you had this chord progression: Cma7 - Amin7 - Dmi7 - G7, you could use only a C major scale to improvise on the progression. That is because all of the chords are in the key of C major (Ima7 - VImi7 - IImi7 - V7). A common progression is IImi7 - V7 - Ima7 and the easiest way to improvise on it in a major key is to use the major scale of the key! So in the key of Bb the progression Cmi7 - F7 - Bbma7 could be accommodated nicely with only a Bb major scale!
In a minor key, you would bracket the II-V-I progression with a harmonic minor scale. So if you had the progression AØ - D7b9 - Gmi7, you could bracket it with a G harmonic minor scale. There is a slight clash of the F# in that scale with the F natural in a Gmi7 but it sounds okay if the F# is treated as an approach tone to G!
Understanding a Tune For Improvisation - Chord Function
Certain chords have to be treated a specific way to sound like they are in the right key! For example, a IImi7 should normally use a Dorian scale. This is because the Dorian scale is the 2nd mode of the major scale of the key. So a Cmi7 in the key of Bb major should use a C Dorian scale which is the 2nd mode of a Bb major scale! If you used a C Aeolian scale, it would include an Ab which is not in the key signature of Bb major! Just the opposite would be true for a Imi7 which requires the Aeolian mode. Again, Cmi7 in the key of C minor requires a C Aeolian scale which has all of the notes of the key signature for C minor. In this case there is an exception. You could use a C Dorian scale to create a surprise because the A natural in that scale is not expected! The Dorian scale is a popular choice for a Imi7 because it includes all of the notes of a minor 13th chord, a good jazz sound!
Another example is a IVma7 which normally should be a Lydian sound. If you have an Fma7 in the key of C major, the required sound is an F Lydian scale. An F major scale includes a Bb which is not in the key signature and would sound strange! By the same token, a Cma7 in the key of C major should be played with a C major scale to sound normal. However, a C Lydian scale could be used to create a surprise since the F# in that scale is not expected. Lydian is a popular choice for major 7th chords because it includes all the notes of a major 13th chord, another good jazz sound!
Understanding a Tune For Improvisation - The Melody
The melody of a song is extremely important for several reasons. First of all, as a simple matter of respect for the composer, you should know the correct notes and rhythms of the melody. Remember that if you play a melody incorrectly, you can be certain someone listening knows the correct melody! You can still develop your own “interpretation” of the melody but you should be faithful to the original! Secondly, the melody is a rich source of material for your improvisation! Just as themes are developed in a classical sonata or a symphony, you can develop fragments of the melody in your improvisation. Thirdly, quoting or embellishing portions of the melody by changing rhythms, adding grace notes or other chromatic embellishment can add interest to your solo.
The most important things about the melody are the implications concerning the sound you should use for improvisation! The melody often contains extensions or alterations of the harmony that may not be expressed in the chord symbol. For example, a G7 with an Eb in the melody implies a #5 or b13 alteration. So, to retain the sound of the melody, which is an essential part of the “aura” of the tune, you should use some scale that has Eb in it! In this case, there are four good choices spelled out below (all include the note Eb):
5th mode of C Harmonic Minor - G Ab B C D Eb F G
G Super Locrian - G Ab Bb B Db Eb F G
5th mode of C Melodic Minor - G A B C D Eb F G
G Whole Tone - G A B Db Eb F G
Sometimes the melody may emphasize the major 6th scale step on a minor chord implying a Dorian scale or the raised 4th scale step on a major chord implying a Lydian scale. Or it may just move through the part of a major scale that includes the natural 4th suggesting a major scale! At any rate, the melody can be very helpful in determining the best scale for improvisation!
Understanding a Tune For Improvisation - Context
In a chord progression, no single chord is set apart from the others. There is always a preceding chord and a following chord. Our memory of what we have been hearing recently is very persuasive on our choice of a scale for improvisation! For example, the progression Cma7 to F7 in the key of C major suggests the use of first a C major scale and then an F Lydian, b7 scale. The Cma7 includes a B natural so our ears like to hear that note continue on the F7 as a #11. Normally, the scale for an F7 would be a Mixolydian scale (F G A Bb C D Eb F) but it includes a Bb which is not in the key of C! In addition, B natural is still in our tonal memory from the Cma7 and, if it can continue, our ears like to hear that happen!
Sometimes we want to anticipate or prepare the sound of the following chord so we will choose a sound that sets up the progression accordingly. For example, C7 to Fmi7 is a V - I in F minor. If we choose a Mixolydian scale on C7, that is the 5th mode of an F major scale and will sound awkward resolving to an Fmi chord. So it would be better to choose a scale for the C7 that includes accidentals that are found in the key signature of F minor. There are two good choices, the 5th mode of F Harmonic Minor and C Super Locrian, shown below:
C7 - 5th mode of F Harmonic Minor - C Db E F G Ab Bb C
C7 - C Super Locrian - C Db Eb E Gb Ab Bb C
Notice that these scales have at least three of the four flats in the key signature of F minor! So the resolution to the Fmi7 sounds very natural.
In general, if trying to decide between two notes that represent two different scale choices for a chord, look to see which one of those notes was in the previous chord! For example, if you were trying to decide whether to play a C Mixolydian scale (includes F natural) or a C Lydian, b7 scale (includes F#), look at the previous chord/scale and see which note was present.
Understanding a Tune For Improvisation - Summary
If you keep these five factors in mind, you should be able to make intelligent choices of the scales needed to improvise on a tune! Sometimes a combination of these aspects may simultaneously suggest the best choice. The chord symbol, melody note and the context may all point to a particular choice. However, often only one of these concepts is needed to see the best sound for a chord! Practice with easy compositions first and graduate to more complicated tunes with more key changes, altered chords, interesting melodies and unusual progressions.
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