Prolation Prolation Prolation is a term used in the theory of the mensural notation of medieval and Renaissance music to describe its rhythmic structure on a small scale, as opposed to "tempus", which described a larger scale. The term "prolation" 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 (whole note) is equal in length to two minims (half notes) ("minor prolation" or "imperfect prolation";
Note value duration, as at the end of a piece (e.g. at the end of Mozart's Mass KV 192). A single eighth note, or any faster note, is always stemmed with flags, while two or more are usually beamed in groups. When a stem is present, it can go either up (from the right side of the note head) or down (from the left side), except in the cases of the "longa" or "maxima" which are nearly always written with downward stems. In most cases, the stem goes down if the notehead is on the center line or above, and up otherwise.