The Key of C, from the Armonía

C major harmonises to C – Dm – Em – F – G – Am – B°; C minor to Cm – D° – Eb – Fm – Gm – Ab – Bb. A son in this key mostly alternates the tonic and the dominant; a ranchera adds the subdominant; a bolero reaches for the submediant and the supertonic on its way home.

Inside the armonía this instrument is the top of the armonía — five re-entrant strings whose open third is the highest open pitch on the instrument, so every strum lands as one tight treble block instead of a spread stack, and the shape below is not a voicing choice so much as a section instruction — the whole armonía strikes the same mánico in unison, on the same slot, or the chord stops being one event.

Learn the tonic, subdominant and dominant in C until the hand goes there unasked, and the repertoire in this key is largely playable before anybody names a form.