McGrath:

Third finger, Sixth string, Ninth fret.
First finger, Third string, Seventh fret.
Fourth finger, Second string, Ninth fret.

There's your D.

'...the essential role of the guitar in Irish sessions, regardless of tunings, is to be a kind of bodhran with strings. It's there to drive, not to lead.'

Well...no. At least, not entirely. I think the mistake that a lot of guitar and bodhran players make is to think that they are there to supply the rhythm in a session. In fact, the rhythm should come from the melody instruments and from the tunes themselves (assuming the melody players are any good).

The two constants for me in Irish music are rhythm and melody. These are generally supplied by melody instruments and the rhythm is supported (not supplied) by the guitar and/or bodhran. If the guitar and bodhran are supplying the rhythm (or 'driving') then you have a problem with your melody instruments.

Where guitars come into their own, for me, is in supplying harmony and the warmth and richness that goes with that. Yes, guitars and bodhrans can complement the rhythm and enrich it (though if I hear one more Samba accompaniment to 'The Silver Spear' someone's gonna be eating soup for a month) but I've always found that the better the melody players I'm with the better I play myself, both rhythmically and harmonically.

I guess some guitar players can hold a session together when the melody instruments are falling apart but it's bloody hard work and frankly I don't find it much fun. Plus at that sort of session you've often got too many thumpers and strummers anyway.