The Key of D — Fiddle

D major harmonises to D – Em – F#m – G – A – Bm – C#°; D minor to Dm – E° – F – Gm – Am – A# – C. Most of the country repertoire in this key lives on three of those chords — the tonic, the subdominant and the dominant — plus the relative minor when a song wants one darker turn.

The fiddle chair carries pads under the verse and the turnaround answer between vocal lines. A chord on a bowed instrument is really a choice of double stops — two strings at a time, drawn from these tones — plus the arpeggio the bow can walk through the rest of them.

Learn the tonic-subdominant-dominant grammar in D until your hand goes there without asking, then add the relative minor, and most of the repertoire in this key is already playable.