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.
What are Diatonic Chords?
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.
Naming the Diatonic Chords with Roman Numerals
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.