Accidentals in Renaissance music have long been a problem for performers and editors, for they are often not fully prescribed in Franco-Flemish music. In the 20th century, a set of 'rules of musica ficta' were assembled to describe performers' practice in the 15th and 16th centuries, but the three primary rules contradict each other when applied to the repertory. The conflict forces one or more rules to be set aside in certain passages. Typically,...