Since the Twelve Tone System is based on the premise that there is no such thing as a wrong note (Only notes that are played wrong) you only need to know certain scales as opposed to the modal approach that is taught by some. The scales you need to memorize are:
Major scales
Melodic Minor scales (ascending only, that is to say in jazz you use the ascending melodic minor no matter what direction your melodic line is going, up or down)
Harmonic minor scales
Diminished scales
Whole tone scales
I practice diminished and whole tone scales for my technique but I rarely use them in improvising as they have no tonal center or key, later I will be discussing these two types of scale again in regards to this lack of tonal center. As for the natural minor scales, since they use the same notes as major scales but starting on a different note, if you practice your major scales over the entire range of your instrument you already know them and the same goes for the Dorian and Mixolydian modes as they are commonly referred to.
I wasn’t going to discuss any theory but on second thought I don’t see any way around it so I am going to talk about some basic theory.
If you look at figure 3 you will see I have written out an Eb Major scale and have placed corresponding numbers beneath each note of the scale. When you are discussing scales it is common to refer to the different notes as numbers which allows you discuss scales without referring to a specific key. For example this allows me to say that if you build a Major 7 chord from a major scale you use the 1, 3, 5, and 7th to create the Major 7 chord. When you stack more notes on top of those the 2 is called the 9, the 4 becomes the 11th and the 6 becomes the 13th. However the 1, 3, 5, and 7th are always the same.
If you look to the right of the Eb Major scale you will see I have written out an Fm7 chord, a Bb7 chord and an Eb Major 7 chord. If you build a chord from the second note of the Eb Major scale you will end up with an Fm7 chord, likewise if you build a chord from the fifth note of the Eb Major scale you will have a Bb7 chord. If you look beneath the Fm7 chord symbol you will see I have written IIm7, under the Bb7 chord V7, and under the EbMaj7 IMaj7, substituting Roman numerals for the chord names. The Roman numerals refer to the fact that the IIm7 is built from the second note of the Major scale, the V7 is built from the fifth note and of course the Major 7 is the built off of the first note. This gives us the IIm7, V7, IMaj7 chord progression which is by far the most common chord progression used in Jazz and popular standards.
The II chord is subdominant, the V chord is dominant and the I chord is the tonic. Basically all western music makes use of the dominant/tonic cycle. The subdominant is rather like a secondary tonic that resolves to the dominant which wants to resolve to the tonic. This cycle of subdominant, dominant, Tonic repeats with modulations to different keys throughout most tunes. Sit down at a piano and play these II,V,I chords and you will hear how the tonic acts as a magnet for the subdominant and dominant chords. You can think of it as a way of establishing a key within the chord progression of a tune.
Not only can you have a II,V,I progression in a Major key you can also have a II,V,I in a minor key which is called a tonic minor. If you look at figure 4 I have written out an Eb harmonic minor scale and to the right have written the corresponding II,V,I chords that have been built from the Eb minor scale. Note there are some differences as the fifth of the IIminor 7 chord is lowered a half step as it is built from a minor rather than a Major scale. This IIminor chord is also called a half diminished chord due to the lowered fifth. For these II and V chords you may use a harmonic minor scale but for the Iminor (with a Major 7) you may use either the melodic or harmonic minor scale. This establishes a tonic minor tonality. In fact if you see a IIm7, V7 leading to a tonic minor, for example Em7, A7, Dm, you should use the corresponding D harmonic minor scale for the II and V chords which gives you the lowered fifth for the II chord and lowered ninth for the V chord.
In figure 5 I have analyzed the chord progression for the song “Just Friends” which basically means I have identified the modulations to different keys. For the purpose of improvising the tonic Major is always a I chord, the minor 7 is always a II chord and the dominant 7 is always a V chord. If the song has a tonic minor the tonic minor is a I chord rather than a II chord and has a raised seventh. You will see I have written the corresponding Roman numeral above the chord symbols as well as the key that section of the song is in, for example – I: Bb, Bb being the key that section of the song is in.
If you look at the last measure of the third and seventh staffs you will see I have also written “pivot chord” beneath the Dm7 chord. The reason for this is that the Dm7 (IIm7) is acting as a tonic minor to the Em7 and A7 chords that precede the Dm7 chord while at the same time the Dm7 is acting as IIm7 due to the G7 chord that follows it. Study the analysis and try it yourself on what ever song you wish. If you have any questions feel free to ask them and I will answer them as I am able.
By looking at the analysis we can see that the song begins in the key of Bb and modulates to the keys of Ab, F, Gb, F, D minor, C, F, Bb, Ab, F, Gb, F, D minor, C, F, and back to Bb again. If this is new to you it may seem complicated at first but once you understand these concepts you will see it is really quite simple, it just takes a lot of verbiage to describe it.
Looking again at figure 5 you will notice I have labeled each 8 bar section of Just Friends with the letters “A” and “B” in boxes down the left hand side. A vast number of songs are written in the standard 32 bar format which in turn is divided into 8 bar sections. The structure of songs can be described by these 8 bar sections, in this case Just Friends has an “A, B, A, B structure. Notice that the chords of both “A” sections are identical with each other and the “B” sections are identical with each other. Another common structure would be “A, A, B, A.” The “B” section is often referred to as the bridge. The true identity of any tune is actually the chord progression, even more so than the actual melody, many Jazz compositions are based on the chord progressions of popular standards. One of the most used was the chord progression of the tune “I Got Rhythm” and many tunes are often described as having I Got Rhythm changes to the point that this progression is instantly recognizable by experienced players.