enharmonic modulation
A modulation that exploits the enharmonic equivalence of a chord to reinterpret it in a new key
In Depth
Enharmonic modulation hinges on a chord that can be respelled without changing its sound. The most common pivot is the German [augmented sixth chord](/term/augmented%20sixth%20chord), which sounds identical to a dominant seventh. By respelling A♭-C-E♭-F♯ as A♭-C-E♭-G♭ (= A♭7), a composer can move instantly from C minor to D♭ major. Similarly, the [diminished seventh chord](/term/diminished%20seventh%20chord) divides the octave into four equal minor thirds, allowing it to resolve to four different keys. These techniques enable sudden, dramatic key changes.
Wagner used enharmonic modulations so frequently in Tristan und Isolde that the opera's tonal centre becomes genuinely ambiguous for long stretches.