Letters added beside neumes in some Western chant notations to clarify or supplement the meaning of the neumes (see Notation, Table 5). They may affect the rhythm, pitch or manner of execution of the neumes. They appear most frequently in St Gallen manuscripts and it was a St Gallen tradition to ascribe their invention to Romanus, a Roman cantor who had brought authentic Roman chant books to St Gallen in the late 8th century; hence the name invented by Schubiger: Romanus-Buchstaben, ‘Romanian letters’. The term ‘significative letters’ derives from Notker’s letter to Lantbert as transmitted in CH-SGs 381 (facs. in PalMus, iv, 1894, pls.B–D) which includes the words ‘quid singulae litterae … significent’. Other significative letters are found in Lorraine and Breton notations.
A. Schubiger: Die Sängerschule St. Gallens (Einsiedeln, 1858)
R.-J. Hesbert: ‘L’interprétation de l’equaliter dans les manuscrits sangalliens’, Revue grégorienne, xviii (1933), 161–73
J. Smits van Waesberghe: ‘Verklaring der letterteekens (litterae significativae) in het gregoriaansche neumenschrift van Sint Gallen’, Musiekgeschiedenis der middeleeuwen, ii (Tilburg, 1942), 285–94
L. Kunz: ‘Die Romanusbuchstaben c und b’, KJb, xxxiv (1950), 7–9
E. Cardine: ‘Les sens de “jusum” et “inferius”’, EG, i (1954), 159
J. Froger: ‘L’épître de Notker sur les “lettres significatives”’, EG, v (1962), 23–72
M.-C. Billecoqc: ‘Lettres ajoutées à la notation neumatique du codex 239 de Laon’, EG, xvii (1978), 7–144