A dorian scale on tenor banjo
The notes of G major centred on A. This is the most common modal key in Irish music, and the reason a minor-sounding tune so often wants a G behind it rather than an E.
Hear the scale, played on the banjo voice
The notes
Every note above sits in first position on a GDAE-tuned tenor banjo: nothing higher than fret 5, and each note has one home. Learn the scale as a shape and your fingers know where every note of every A dorian tune lives before you have heard it.
The chords that go with it
This is the connection that makes session playing make sense. The backer's chords are built from the same 7 notes as the scale, so when the guitar holds Am, anything you play from the A dorian scale fits. Melody players who seem to improvise freely are doing exactly this: decorating the tune with notes that never leave its own scale. Shapes for every chord here are on the tenor banjo chord page.
Dorian is a minor sound with a sharpened sixth. It uses exactly the notes of a major scale but centres two steps higher, which is why the chords behind it come from the major key, not from classical minor harmony.
Tunes in A dorian
45 of the 2701 tunes on this site are recorded in Ador. A dozen to start on, in alphabetical order - every one has free GDAE tab, playback and the ABC source.
Questions about A dorian
A, B, C, D, E, F#, G, A. On a GDAE-tuned tenor banjo the whole scale sits in first position, between the open strings and fret 5.
Am, G, C carry most tunes in A dorian, with Em, D as passing and turnaround chords. Two or three chords are enough: Irish accompaniment stays out of the tune's way.
In an Irish session the chord follows the tune, not the other way round. If the tune is in A dorian, every note of the scale above fits over its chords, including Am and G and C. That is how melody players improvise variations without reading anything: they stay inside the tune's own scale.
This site's collection has 45 tunes recorded in Ador out of 2701 in total, each with free GDAE tab. The corpus is O'Neill's 1903 and 1907 collections plus Kerr's Merry Melodies, so the balance reflects the tradition as it was written down.