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Section 23.1 Enharmonic Modulation

In an enharmonic modulation, the pivot chord is almost always misspelled in one of the keys and therefore must be reconceptualized enharmonically by the analyst. In this regard, an enharmonic modulation is a harmonic pun.
Here is a pun from Shakespeare’s Richard III, Act 1, Scene 1:
Now is the winter of our discontent
Made glorious summer by this sun of York
The “sun” of York is the son of York, King Edward IV.
Here is a simple enharmonic modulation:
Figure 23.1.1. Enharmonic Modulation from C major to B minor
Like a verbal pun, this harmonic pun is effective because the third chord (\(\left.\text{G}^{7}\right.\)) has two “meanings”—in the context of C major, \(\left.\text{G}^{7}\right.\) is \(\left.\text{V}^{7}\right.\) and the root wants to cadence down a fifth to C, but the \(\left.\text{G}^{7}\right.\) is a \(\left.\text{Ger}^{+6}\right.\) in the context of B minor, where the root of the \(\left.\text{G}^{7}\right.\) wants to progress down a half step to a chord of dominant function, \(\left.\text{i}^{6}_{4}\right.\) in the example above.
Figure 23.1.2.
Notice that the \(\left.\text{G}^{7}\right.\) can only be spelled correctly in one of the keys—either as a dominant seventh chord on G (G–B–D–F) or as a \(\left.\text{Ger}^{+6}\right.\) on G (G–B–D–E♯), hence the term “enharmonic modulation.” The analyst must envision the other spelling (the one not shown) to understand the double context, in the same way “sun of York” must be envisioned as “son of York.”
We will encounter two sonorities used in enharmonic modulations: the dominant seventh sonority and the diminished seventh sonority.