<P> Polytonality (also polyharmony (Cole and Schwartz 2012)) is the musical use of more than one key simultaneously . Bitonality is the use of only two different keys at the same time . Polyvalence is the use of more than one harmonic function, from the same key, at the same time (Leeuw 2005, 87). </P> <P> Some examples of bitonality superimpose fully harmonized sections of music in different keys . </P>

The technique of using two or more tonal centers at the same time is called