Köln, Erzbischöfliche Diözesan- und Dombibliothek 127, fol. 10v

Gratian,  Decretum, D.4 d.p.c3:  Leges instituuntur cum promulgantur, firmantur cum moribus utentium approbantur.  (Laws are established when they are promulgated and confirmed when they are approved by the long standing customs of those who obey them).

Justinian, Institutes 1.2.9: Nam diuturni mores consensu utentium comprobari legem imitantur (cf. Gratian, Decretum, D.12 c.6)

Consuetudo (Costume)   Mos (?)