The Key of D — Mandolin

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 mandolin chair carries the chop on the backbeat — a closed, muted chord landing where a snare would, and a chop is a chord with the ring taken out of it — closed shapes only, damped the instant they sound, landing where a snare would.

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.