Polytonality is a musical compositional technique in which a composer uses two or more keys at once rather than just one. One player may, for example, perform in C major while another performs in E flat major. Each key has a tonal center, which is usually the first note of the scale associated with that key. The composer establishes multiple tonal centers using more than one key, which in theory makes the music more complex and interesting for the listener.
Polytonality is based entirely on tonal concepts that have existed for hundreds of years, despite the fact that musicians tend to classify it as a more contemporary musical method. In fact, because keys are only suggested or implied at best, more contemporary atonal music, which does not use tonal centers at all, cannot be technically polytonal. As a result, it’s preferable to think of the technique as a creative way to achieve a contemporary sound without breaking tonal rules.
Because polytonality is so noticeable, composers use it only when they want to make a strong statement and put a modern spin on traditional tonality. However, because the multiple keys always end up harmonizing each other in some way and thus are never truly independent, the degree of polytonality is dependent on how closely the selected keys are related. For example, if F major and A major were used in a work, the relationship would be a third interval, which is consonant and very common. The interval would be an augmented or raised fourth if a composer wrote in F major and B major, which is a less common, dissonant interval that stands out much more to the ear.
Polytonality was first used sparingly and primarily for comedic effect composers like Wolfgang Amadeus Mozart. Later, composers used polytonality to emphasize that a certain amount of musical chaos could result in a pleasing greater whole. These composers believed that what makes music interesting is dissonance, counterpoint, and “fighting” between players or sections. Charles Ives, whose famous “Variations on America” is hailed as a polytonal masterpiece, was one of the greatest composers in this regard.
Polytonality does not have to be present throughout a piece of music, though it may be. Players playing the same melody in parallel motion, starting on two different pitches, is probably the simplest example of this. It usually happens when the composer is trying to build up to a climax.