Harmonic ambiguity
Possibility of assigning a note, interval, or chord to different keys depending on context, for instance enharmonically.
What it means
Harmonic ambiguity is the name for the possibility of assigning a note, interval, or chord to different keys or functions depending on context. One and the same sonority can thus be interpreted in several ways, for instance enharmonically, when the same keys are notated and understood differently.
Musical use
Composers use ambiguity for modulations: a chord that makes sense in the old and the new key serves as a pivot and leads unobtrusively into the new key. Especially ambiguous are the diminished seventh chord, which can be resolved into four keys, and the augmented triad, which consists of equal thirds and has no definite root. They are means of Romantic and later harmony, in which boundaries between keys blur.
Harmonic ambiguity should be distinguished from modulation proper, the actual change of key, and from alteration, which chromatically changes a chord tone. Ambiguity denotes the possibility of several interpretations, not the movement itself.
Performance practice
In a piece, listen for passages where the harmonic direction changes surprisingly, and ask what sonority you had earlier heard as dominant, leading tone, or intermediate step. Shape such sonorities in performance open and floating so that their double meaning stays audible before they decide on a resolution.