When speaking of music and harmony, you will frequently encounter the term diatonic. It’s important to understand its meaning. You’ll be applying this concept all of the time whether you realize it or not.
When we use the musical term diatonic, we mean the notes being used all come from the key. In that way the terms diatonic and key mean much the same thing.
For instance, the key of C major contains the seven notes of the C major scale – C, D, E, F, G, A, and B. Any music said to be diatonic and in the key of C only uses combinations of those 7 notes from C major.
If a melody is said to be diatonic and in the key of C, it only uses the 7 notes of the C major scale/key.
If a chord progression is said to be diatonic and in the key of C, all of the notes used to build the chords would come from the notes of the key of C major. So, an F major triad would be a diatonic chord in the key of C because F major contains the notes F, A, and C – all notes within the key. An F minor triad contains the notes F, Ab, and C. Since the key of C does not contain an Ab, F minor is not a diatonic chord in the key of C.
Diatonic Harmony and Music
A lot of music is purely diatonic. Purely diatonic music has a simple, straightforward sound to it. For instance, folk songs and nursery rhymes are often strictly diatonic.
More often, songs are mostly diatonic only straying from the notes of the key once in a while.
In order to fully understand music containing non-diatonic notes, you first need to understand basic diatonic harmony. Diatonic harmony is the study of how notes within a key relate to one another.
In this lesson my aim is to give you a very rudimentary understanding of how musicians often think of chords and chord progressions. This lesson is just a preview of these concepts. Please don’t feel lost or overwhelmed. I always like to plant the seed of a concept in your mind first and, later on, follow up on it more thoroughly.
Diatonic chords are the chords that are derived from the notes of a key.
You should think of diatonic chords as a family of chords all tied to one another by the notes of a key. They all sort of share the same gene pool.
We’ve established that each key contains seven different notes. It is possible to build a chord on each of the seven notes in every key. Each note of the key serves as a root note for a chord. Therefore each key has 7 basic diatonic chords.
You should remember that the notes of the major scale were numbered Root (or, 1), 2, 3, 4, 5, 6, and 7. We called these scale degrees. When we discuss diatonic chords we name them with Roman numerals corresponding to the scale degree on which each chord is built.
In practice we use uppercase roman numerals to indicate major chords and lowercase to indicate minor chords. There are some other symbols sometimes added to the Roman numerals, but we’ll get to them later
If you remember from a previous lesson on what is a chord there are 4 types of Triad chord formed from using the Root, the major or minor third and the diminished, perfect, or augmented fifth.
We also know that that a major third is 2 whole tones or 4 half tones, and a minor third is a whole tone plus a half tone or 3 half tones.
Look at the diagram above, step from left to right equals a half tone. So a major 3 third would be 4 boxes and a minor third would be 3 boxes.
Diatonic Major Scale Formula
Root + 2 + 2 + 1 + 2 + 2 + 2 + 1
fret fret fret fret fret fret fret
C D E F G A B C
Since our triads need either four fret or three fret distances and the major scale is built in 2 fret and 1 fret distances we must skip every other note of the scale when building triads(chords). The three pitches of the chord built off of the first pitch of the scale (C) will be C E G. The three pitches of the chord built off of the second pitch of the scale (D) will be D F A. The three pitches of the chord built off of the third pitch of the scale (E) will be E G B. This process will continue until every pitch of the scale has a triad built off of it.
The next step is to count the distances between the pitches of each triad to find out what kind of chord it is (major, minor, diminished, or augmented). Here is a table showing this information for the key of C major:
R + 2 + 2 + 1 + 2 + 2 + 2 + 1
All Diatonic Major Scales are built with the same formula of fret distances. So whatever we discover about the types of chords built off each step of the key of C major is true about every major scale. The first chord in every key is major, the second chord in every key is minor, the third chord in every key is minor, and so on just like our example the key of C major.
The next step is to understand how these seven chords relate to each other in the hierarchy of chord progressions. Music gains its ability to move people from the dynamic polarity of expand and contract. Expansion means certain chords in the key move the listener away from the key center (home). These are called Dominant preparation chords and begin to build tension by moving away (expanding) from the Tonic (home/rest).
Contraction means certain chords in the key drive the listener back to the key center (home). These are called Dominant chords and maximize the tension which is released by returning to any of the Tonic functioning chords.
Each of these three groups of chords have at least two levels of strength—primary
(strongest) and secondary (weaker). The chord built off the sixth step of the scale can function as either Tonic or Dominant Preparation. This chord is also the tonic of the relative minor scale—a major and relative minor scale share the exact same seven pitches and are a simple rotation of each other.
C major - C D E F G A B C - Relative to - A minor - A B C D E F G A
Here is a chart which shows the three functions, their primary and secondary chords, and multi-functioning six minor chord. There are two directions through this chart:
The Path of Progression—This path has always been considered the proper direction by classical theorists because of its progressive feeling of tension/climax/release.
The Path of Retrogression—This path is relatively new and was ushered in by the 20 century.
It seems to speak of the decaying of the evolutionary process. Retrogression has been considered a no-no by classical theorists because of its feeling of leaking tension. It is a mainstay of the basic 12 bar blues progression and can be found in much of pop culture’s music.
The human condition is a complex and ever changing ocean of feelings and situations lending to the use of both paths depending on the composer’s need to communicate a particular point of view.
A Progression is created by moving from the I chord to any other chord and back to the I chord. The is because of the complete feeling of rest the I chord creates.
A Deceptive Cadence is created by moving from a Dominant functioning chord to the vi minor chord because of its resolution of the tri-tone (4th and 7th steps of the major scale—the two naturally occurring half steps).