The Key of Bb, from the Armonía

Bb major harmonises to Bb – Cm – Dm – Eb – F – Gm – A°; Bb minor to Bbm – C° – Db – Ebm – Fm – Gb – Ab. 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 Bb until the hand goes there unasked, and the repertoire in this key is largely playable before anybody names a form.