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2. HOW TO IMPROVISE OVER A CHORD
This question will be explained by means of an example. Suppose that we want to improvise over the Em7 chord. Firstly, we have to know the context in which this chord is located. For instance, if around this chord (that is, ahead or behind it) we find such chords as C , F, Dm7, G7, etc., we can use the C Major scale (and its corresponding modes) to improvise on all these chords, since all of them belong to the C Major scale.
On the other hand, if around Em7 chord we find such chords as Bm, D+, F 7, A , etc., we can use the B harmonic minor scale to improvise on all these chords, since all of them belong to this scale. But it can also occur that, around Em7 chord, we find such chords as Dm, F+, G7, C , etc., in which case we would use the D melodic minor scale, since all these chords belong to this scale.
Note that, in all these examples and other similar ones than can be introduced, the chosen scale for improvising always contains all the notes in the Em7 chord, that is, E, G, B and D.
Although determining the context in which a chord is located requires certain experience, the Harmonic Wheel can help a lot, mainly at the beginning, as it allows to quickly visualize all the chords belonging to a given scale. Thus, checking the previous examples with the Harmonic Wheel is really simple.
Logically, the key signature itself will determine, in most cases, the scale we can use to improvise. However, we cannot fully trust it, since most works contain brief modulations or, simply, altered chords, where the key signature remains, but the scale does not. Therefore, it is always better to analyze the existing chords in each part or passage of the score.
But on the other hand, there are special situations where it is desirable to use other scales different from the above. Among these situations, we can point out the following:
- When the same chord lasts several bars. In this case, using only one scale can be monotonous. And even more, if several improvisations are going to be carried out on the same chord progression.
- When we wish to introduce a different sound on certain chords. This is very common, for example, in Dominant 7th chords, where it may be interesting to augment or reduce the “dissonance” or “tension” this chord presents. This can be achieved by using different scales for improvising.
This way, we arrive to a very general question: Which are the available or most suitable scales for improvising on a given chord? Even if there are no strict rules in Music, as it has been stated several times, we can say that, from a purely logical point of view, the most suitable scales for improvising on a given chord are those containing the notes of the chord.
This means that, if we go back to the Em7 chord, which is composed by notes E, G, B and D, the available scales for improvising on it will be those containing these four notes. Thus, the C Major, G Major or D Major scales will be good candidates for the improvisation, as they contain these notes. On the contrary, the F Major or A Major scales, for example, will not be suitable for it, as they do not contain the notes of this chord. In fact, it can be proved that there are only 3 Major scales containing the notes of Em7 chord; precisely, those above mentioned.
Besides the Major scales, we can search for minor scales that fit to this chord. The E harmonic or melodic minor scales, however, would not be suitable since they contain the sharp D instead of natural D. (Let us remember that, in this context, it is assumed that the melodic minor scale is that having the 6th and 7th degrees raised one half step, both ascending and descending). On the other hand, the B harmonic minor and D melodic minor scales are suitable for this improvisation, as seen previously. In fact, it can be proved that there are no other minor scales containing the notes of Em7 chord. (We do not consider here natural minor scales, for they are equivalent to their relative Major ones). Fig. 1 shows the relationships among all these scales and the Em7 chord.
Figure 1. The Em7 chord and some of its associated scales.
As we can notice, knowing the scales containing the notes of a given chord is not easy at all. And the difficulty increases when this chord is related to scales having 5 or 6 accidentals in the key signature.
We must take into account that, besides the minor 7th chords, as that considered in the example, there are other types of chords, such as the Major 7th, the Dominant 7th, the diminished, the half-diminished, etc., just for citing some 4 note chords. Moreover, there are 5 or 6 note chords, which include the 9th, the 11th or the 13th, which in turn may be altered one half-step up or down.
This way, we obtain a big set of chords, but all of them are very used, mainly in Jazz compositions. And, for any of them, we need to know which scales are most suitable for improvising.
In order to complete this panoramic view of improvisation, we can add that the scales used to improvise are not limited to the Major, harmonic and melodic minor scales, but some other types of scales are used as well, such as diminished, Whole Tone, Pentatonic, Bebop, etc. All of this increases the improvisation complexity, as well as our interest in it.
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