Among the theories prevalent in the middle ages was one that mankind formed a unity, with the pope and the emperor at the head of it: the universal Church and the universal emperor ruled the world (Rehm, Geschichte der Rechtswissenschaft, p. 198.) Even to Leibnitz, writing in the 17th century, it seemed that "totam Christianitatem unam velut Rempublicam componere, in qua Caesari auctoritas aliqua competit" (Opera, 4.330).
In the Cluniac circle was coined the principle: Canonica auctoritas Dei lex est, canon law being taken in the Pseudo-Isidorian sense.
Aristotelian dialectics had always been taught in the schools; and reason as well as authority had been appealed to as the foundation of theology; but for the theologians of the 9th and 10th centuries, whose method had been merely that of restatement, ratio and auctoritas were in perfect accord.
It is possible, though far from certain (see Senate), that the powers of the interregnum and the senatorial confirmation (patrum auctoritas) necessary to give validity to decisions of the people, remained the exclusive privileges of the patrician members of the senate.
"Auctoritas siquidem ex vera ratione processit, ratio vero nequaquam ex auctoritate.
Omnis enim auctoritas, quae vera ratione non approbatur, infirma videtur esse.