The Key of F — Mandolin
The tonic, subdominant and dominant chords, and what this chair plays across them.
F major harmonises to F – Gm – Am – A# – C – Dm – E°; F minor to Fm – G° – G# – A#m – Cm – C# – D#. 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 F until your hand goes there without asking, then add the relative minor, and most of the repertoire in this key is already playable.