The Diatonic Scale
Intervals between notes that form the scale of a particular key are said to be diatonic. This applies to major and minor scales. Notes that are not part of these scales are said to be chromatic - those notes are chromatic notes.
Let us look at a few examples.
In the key of C the notes C, D, E flat, E, F, G, A flat, A, B flat and B are diatonic because they appear in one or more of the major, natural minor, melodic minor or harmonic minor scales. In this key, any other note will be chromatic.
When examining the relationship between notes, the key is a vital element. In the key of C, D sharp will be a chromatic note. However, in the key of E, both C and D sharp are diatonic because both appear in the scale of E harmonic minor.
We have more to say on this in the next lesson.
Do not confuse chromatic notes with chromatic scales. We have already met the chromatic scale, one example of a symmetrical scale, those constructed from a repeating pattern of intervals (in this case, a semitone or half-step). Some notes of a chromatic scale are chromatic to the key note (in this case the first note) while others are diatonic. We will meet other symmetrical scales in lesson 25.
The terms diatonic and chromatic can be extended to any groups of notes, musical phrases, scale passages, chords and harmonies as we shall find later. What is important is that diatonic passages tend to have a sense of key about them. When chromatic notes are introduced, the sense of key is generally weakened.