Azo, Summa Codicis 1.14, Cologny, Fondation Martin Bodmer, Cod. Bodmer 14, fol. 6r (ca. 1250)

Azo (ca. 1200-1220), Summa Codicis, De  legibus et constitutionibus principis Cod. 1.14, Aschaffenburg Stiftsbibliothek Perg. 15, fol. 4v, (Lyon 1564) fol. 8r, Cologny, Fondation Martin Bodmer, Cod. Bodmer 14, fol. 6r-6v
Lex autem ponitur quandoque stricte quandoque large, stricte ut cum ponitur pro statuto populi Romani, et hoc est quod dicitur lex est   .   .   .  Lex est commune praeceptum virorum prudentium  .   .   .   Quandoque ponitur large pro omni rationabili  statuto.  Vt et dicitur lex est sanctio sancta, iubens honesta prohibens contraria.  Et ita regula est  iustorum et iniustorum, ut dicitur in translatione greci, ut ff. eodem l.ii. (Dig. 1.3.2). (Lex moreover is used sometimes narrowly and sometimes broadly, narrowly as when it is used to describe a statute of the Roman people, and this is what is said is lex .  .  .  Lex is the general command of prudent men .  .  . Sometimes lex is defined broadly  as in all reasonable statutes.  Whence lex is called a pious ordinance, commanding right actions and prohibiting wrong.  Thus lex is a rule of the just and the unjust, as is stated in the translation of the Greek in the Digest.)

Lex is a perfect term suited to the jurisprudence of legal positivism (John Austin)