Romans in effect considered that a ‘nature of things’ (ordo rerum) exists, a «arrangement of the elements of the universe and of institutions, as Gods have conceived and set it up », and that « the nature of religion consists in preserving it against all that it is seen as a blow : eclipses, twins or albino people, wonders, etc..» (Roger Caillois, ibid., op. cit.).

Gods are committed by the ritual answer, as far as this one is appropriate. As Gods and mankind are somehow linked by mutual obligations, religion may be seen as the source of Law.

Universe is also a invisible thread, which may be revealed thanks to signs that are to be unveiled and that tell us what must be done to « go in the right direction ». The omen is one of these signs. It is a « sentence pronunced by a third person in a specific intent, but which can litteraly apply to the problems and to the behavior of this individual, and then constitutes a sign which may inspire fear or trust. » (Raymond Bloch).

An exemple of omen is the one received by Crassus, when leaving to fight Parthians, from a figs seller. The Caunian (sic ! - Caunus, Asia Minor city) shouted him: "Cauneas!". It is to say : «Buy !» (ficos : figs). In fact, it was a warning that should have been heard :
«Caue ne eas» : «Care, do not go». Crassus did not understand the omen and lose life, son and legions in Carrhae.

With times passing by, the augurs felt free with regard to relations and interpretations written in in thick «commentaries» and doctrine books.

At last they decided themselves, for instance, of the wideness of the zone that might include the signs to be interpreted, they decided these signs themselves and the right moment to make the statement and the interpretation. They have thus contributed to establish the concept of auctoritas (i.e. what gives value to an act), a key one in roman politics life.