Guárdame las vacas (Otras tres diferencias) by Luys de Narváez
Otras tres diferencias hechas por otra parte.
Guárdame las vacas is a villancico more than half a millennium old. Its basic structure consists of a repeating bass part overlayed with a descant. A villancico literally being peasant music, it's quite possible the bass part was commonly played by strumming chords while the words were sung to the descant. Over time we've come to associate the piece with the bass part only, which in A minor would be: C–G–Am–E / C–G–Am–E–Am (III–VII–i–V / III–VII–i–V–i). Narváez's first four variations feature the bass part prominently, leading one not to recognize fully the presence of the descant despite its integral contribution to the variations.
Narváez, however, composed a set of three variations on the descant using a different bass part known as a passamezzo antico in Italian. He labeled these as Otras tres diferencias hechas por otra parte in Los seys libros del Delphín, a book of vihuela music notated in tablature. It's not entirely clear if the otra parte (other part) refers to the treble part of Guárdame las vacas or the other bass part used as the ground for the second set of variations. Despite being in different keys, it is the descant that connects the two sets of variations. Each should be treated as a separate set of variations and not as part of a single combined piece. But one should be aware that the pieces share in common the descant, making each a version of Guárdame las vacas.
I transcribed this piece from the original vihuela tablature, using a copy of Los seys libros del Delphín (1538) from the Biblioteca Nacional de España. For a time, it was fashionable to interleave the first of the three variations into the set of four variations. This was done by transposing the piece into A minor, an approach presumably popularized by Andrés Segovia, who would play it thus, usually as an encore. Although it is certainly a valid artistic choice to arrange the music in such a manner, doing so has misled many a listener as to the nature of the original work in addition to depriving the world of hearing the two remaining variations from the second set. Julian Bream rectified this trend by recording the two sets of variations separately, albeit on the lute. My transcription is for the guitar and does not require you to retune the third string to F♯. It also does not change the key, leaving it in D minor.
Whereas the first set of variations in A minor are easily played in standard guitar turning, these three variations can be a little awkward at times. If you don't care for the fingering, try alternatives that work better for you or tune the third string to F♯ if you think it would simplify playing the piece.
Removed a slur from measure 6.
Changed last D in first voice of measure 8 to use finger 4.
Added slurs to measures 25–27.
Updated fingering and added guitar-specific legato. Changed beaming to match metrical changes.
First draft. Contains notes and initial left-hand fingering. Later revisions may correct discovered errors, change fingering, and add guitar-specific legato where appropriate.
 The bass part appears in many compositions and is known as the romanesca in Italian. In Spain, it was so closely associated with the song that it was known as Guárdame las vacas. At the time, the harmonic pairing of the bass part and the descant was associated with those names.
 Strictly speaking, the music is modal and not conceived of as being in a specific key, but instead as being built on hexachords.