Gabriel Furtado
https://www.cglib.org/analysis-of-vi
It is clear that these twelve studies were intended to be a complete set instead of just independent works that Villa-Lobos composed separately and only later compiled. This is clear because the etudes follow harmonic pattern of an extended circle of fifths. This begins quite simply movement throughout the keys in the first half of the etudes, but in the second half the relationships become a bit more convoluted. As guitarist David Tanenbaum notes “the final note (as in nos. 7 and 
or chord ( as in nos. 9 and10) of one etude can act as a kind of dominant to the next.45 Apart from the harmonic material, there seems to be a deeper cognitive division between the first half and the second half of the piece; The first half use Italian expression marks, while the second half use French markings. While this points to a shift in Villa-Lobos’ thinking, it is unclear as to what the significance is.
With regard to the compositional materials used, the influence of both choro and French impressionism are evenly distributed throughout the works. The studies make ample use of quartal and quintal harmonies and planing as well as –to a much lesser extent- bitonality, whole-tone passages and modes. When considering on whether or not Villa-Lobos employed these techniques specifically to invoke the French impressionism, one is presented with a chicken-and-the-egg sort of problem. Both quartal and quintal harmonies occur naturally on the open strings of the guitar. Bar chords, which allow a guitarist to play many chords using the same hand position, are an essential tool for guitar harmony that moves chords around without changing the voicing, thus resulting in parallel motion. The question then becomes, did Villa-Lobos use these compositional devices because of his contact with French impressionism, or was it simply a matter of necessity for composing on the guitar?
