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 bottom of the armonía — the same mánico the vihuela is playing, an octave lower and with more sustain, which is what stops the section sounding thin under a full melody. Nothing here is a solo grip: the value of the shape is that it lines up with the vihuela's, so the pair arrive in unison as one attack with a low half and a high half.

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.