Prolation
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Prolation is a term used in the theory of medieval music to describe its rhythmic structure on a small scale. The term is derived from the Latin prolatio, first used by Philippe de Vitry in describing Ars Nova, a musical style that came about in 14th-century France.
Prolation, together with tempus, corresponds roughly to the concept of time signature in modern music. Prolation describes whether a semibreve is equal in length to two minims (minor prolation or imperfect prolation) or three minims (major prolation or perfect prolation).
Early medieval music was often structured in subdivisions of three, while the note values in modern music are unambiguously subdivided into two parts, meaning that only minor prolation has survived in our time signature system. We now indicate subdivisions of three by modifying note values with dots or triplets. The history of written medieval music shows a gradual shift from major to minor prolation being common.
