The Key of C — Bass

C major harmonises to C – Dm – Em – F – G – Am – B°; C minor to Cm – D° – D# – Fm – Gm – G# – A#. 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 bass chair carries the root-and-fifth pulse everything else in the arrangement is timed against. Almost none of a chord is playable down here and almost none of it is wanted: the mix hears whichever note sits at the bottom as the chord, so the choice is which one, and when.

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