Polytonality in music theory

Polytonality or Polyharmony

Polytonality or polyharmony, is the practice of using two or more keys at once in a musical composition. It is a similar concept to polyvalence or polyvalency, which is the use of more than one harmonic function simultaneously, but in the same key.

The key centers are chosen for their dissonant or consonant characteristics when juxtaposed. An example of a dissonant relationship is when there are fewer than five shared pitches between the keys. Conversely, a consonant relationship is when five or more pitches are present in the keys.