A Dictionary of Music and Musicians/Proprietas

PROPRIETAS, propriety (Germ. Eigenheit). A peculiarity attributed, by Mediæval writers, to those Ligatures in which the first note was sung as a Breve: the Breve being always understood to represent a complete Measure (Lat. Tactus; Old Eng. Stroke). Franco of Cologne describes Ligatures beginning with Breves, Longs, and Semibreves, as Ligaturæ cum, sine, and cum opposita Proprietate, respectively.

[ W. S. R. ]