Diatonic harmony refers to the music elements ie; Chords/Arpeggios,Modes derived from the major scale.
In this example, Im choosing the key of C which notes are C D E F G A B C
also, the chords and arpeggios that derive from diatonic harmony. You must stay in the key and play each Mode and chord from the particular key.
Here’s an example:
You’ll notice that all the notes that make up each arpeggio are in the C major scale and constructed on either a major 3rd interval or a minor 3rd interval. for more on this topic visit my web site tonycimorosi ENJOY