• Getting familiar with diatonic thirds can really open up your understanding of the guitar neck, modes and harmony. It's a great way to add more interest to your soloing.
• In Ionian (major scale), the order of the thirds is Maj. Min. Min. Maj. Maj. Min. Min. (and back to Maj.). But I think it's best to think of it as a circle.
• Just remember you'll never play more than 2 Majors or 2 Minors in a row.
• In this lesson I use D major, because it starts near the nut but uses no open strings (and is therefore movable).
• D Ionian = A Mixolydian = Em Dorian = Bm Aeolian. Therefore, you can play the D Major series to all 4 backing tracks!
• Though the notes are the same, each mode has a different "tone center."
• The goal is to get so familiar with the series that your ear tells you if the next third will be major or minor.
• In actual use, combine diatonic thirds with other scales, arpeggios, licks, lines, rhythms, etc.