Polytonality
（重定向自Bitonalities）
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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).