In harmony with enharmony
It is a truism that there are always new things to find on an instrument. I was reminded of this transcribing a song by Elvis Costello for a guitar student.
The song featured a rising bass line where an inverted chord was succeeded by a root chord. Such bass-lines are common in more sophisticated songwriting, enjoyed by songwriters and listeners alike for the feeling of mobile ingenuity they convey. I found myself looking on the guitar for a playable G# chord with B# as the bass note. G# major is usually fretted (466544) with a standard barre chord. Initially, I couldn’t find one where B# would be the lowest note – and then saw a solution by using enharmonic equivalence.
It’s a simple concept. Western music has 12 notes, five of which have two names each. They are enharmonically equivalent. These are the sharp / flat notes (A#/Bb, C#/Db, D#/Eb, F#/Gb. G#/Ab), the black keys on a piano. Which name is used depends on musical context, and sometimes this has significant musical consequences.
I found the shape I needed by thinking of G#/B# as its enharmonic equivalent Ab/C. Straightaway this shape – x3111x – presented itself and fitted nicely into the sequence. Problem solved.
In classical music composers make inventive use of this kind of substitution on a grand scale. The first movement of Vaughan Williams’ Symphony no 5 (1943)
begins ambiguously hovering between tonalities of D and C. At 2:15 the music darkens into an overcast C minor before achieving a startling and joyous shift into E major at 3:22, as though the sun had broken out. The keys of C minor and E major are distant from each other – three flats versus four sharps – so it would seems that moving from one to another might be a big step. To establish the key of E major the note D# is important. But how can it appear in C minor? The answer is the note is already there, disguised as the enharmonic, Eb. By treating the one note differently the key change is facilitated.