Diatonic harmony is the most natural choice to start jazz theory. Let’s start with the C major scale that consists of the white keys of the piano. C major scale starts and ends with C and it is called Ionian mode in modal harmony. We will give examples of modal harmony in this post as well. We are using alphabetical names of notes which is quite popular in jazz world.
Do=C, Re=D, Mi=E, Fa=F, Sol=G, La=A, Ti=B.
Even though Do is the first note in Do major scale, La is the first note on the piano. That is why A is assigned to La.
We will start our theory with 7th chords since tri-note triads are rarely used in jazz. 7th chords of C major scale are listed at the picture below. You can follow how the chords are constructed from my post that is titled ‘Building blocks of chords, intervals’. In the mean time you can see the quality of the 7th chords in the picture below that was built from each note of C major scale as the root.
These chords are built from the white keys of piano. They are started with a root note and completed with 4 notes skipping a white key between chord tones. For example, if our first root note is a C, then our chord consists of the C-E-G-B notes. The quality of this chord is major 7th. The reason behind this naming convention is explained in my post that is titled ‘Building blocks of chords, intervals‘. Since our second chord’s root note is D, this chord could be completed with D-F-A-C notes based on the previously mentioned formula. The chord quality of the first, second and third chords etc… will always be the same for all of the major scales. Meaning, the first chord of a major scale will be a major 7th while the second chord will be a minor 7th. To simplify this harmonic math, Roman Numeric System was widely used in jazz. Major scale chords are listed as follows in Roman Numeric System:
Imaj7 – IIm7 – IIIm7 – IVmaj7 – V7 – VIm7 – VIIm7b5.
m7 ( minor 7th ) chord was also shown as -7 in jazz ( II-7, III-7 ).
The other modes in C Major scale are as follows:
Dorian mode, can be used over II-7 chord.
Phrigian mode, can be used over III-7 chord.
Lydian mode, can be used over IVmaj7 chord.
Mixolydian mode, can be used over V7 ( dominant 7th ) chord.
Aeolian mode, can be used over VI-7 chord.
Locrian mode, can be used over VII-7b5 chord.