DADGAD Guitar - Leaving Out the 3rd

Go Guitars Type II Parlor Guitar

Irish backup accompaniment - whether it's on guitar, bouzouki, or some other instrument - is a mystery to me.  Which is why I'm glad I play melody.  Although I do think it's good to have some idea of what the other instruments in the ensemble are doing.  This can help you play your own instrument better.

For this reason, I was searching online about DADGAD guitar last weekend.  All I really knew about DADGAD guitar was that it was an open tuning and that you often leave the third of the chord.  I know enough basic music theory to grasp what leaving out the 3rd means.  The 3rd is the note that makes a chord sound major or minor.  The notes in a D chord are D, F# and A, with F# being the 3rd.  When you leave out the 3rd it gives the chord a droning, power chord quality that suits Celtic music.

What I didn't know was what you replace this note with.  I found a page devoted to DADGAD guitar that suggests there is a formula.  Michael Eskin says that as a general rule, when in DADGAD he replaces the 3^rd of the chord with either the root, the 5^th, the 7^th or 9^th depending on what's easiest to play, what suits the melody, and/or what reinforces the tonal root of the tune.

For the D chord you would replace any F#’s in your typical chord shape with one of the following notes:  D, A, C or E.  (D is the root note, A is the 5 of the chord, and C or E are the 7 or 9 notes one whole step away on either side of D).  It doesn’t really matter if you are doubling up or tripling up the D or the A notes – that helps the root tone of the chord ring out.  If you can get by on just the notes D and A for your "D" chord - such as DDDAAD - those will work fine.

A Gmajor chord would typically use the notes G, B and D.  Using this same formula, when you need to make a G chord in the key of D you’ll remove the B note and replace it with either G, D or A.  Why A?  Because this G chord is being used in the role of the IV chord in the key of D, using an A note makes sense because the sound of the A will reinforce the D note to which the tune centers around and resolves to.  GDDGAD.

This might be an oversimplification, and there's a good chance I misinterpreted the instructions.  At the very least, I think I know know a little bit more than I did before.  I would like to hear what others thoughts are on this.

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