In the introduction to Niall Rudd’s Oxford World’s Classics translation of what survives of Cicero’s Republic and Laws, 1 Jonathan Powell and Niall Rudd include a section on natural law, which for Cicero stands above all civil and positive law. There they note that Cicero’s view of natural law rests on other commitments, “certain fundamental beliefs” (xxvii). They helpfully lists what those are in their view (xxvii-xxx). What are the necessary assumptions for Ciceronian natural law?
1. That the universe is a system run by a rational Providence.
2. That Mankind stands between God and the animals.
3. That human potential can only be realized in communities.
4. That man is a distinct species. (By this, he means that, in spite of differences in nationality, custom, etc., “Man represents a single concept, embraced in a single definition” [xxix]. Thus, because of this unity of species, all men everywhere are subject to the natural law.)
5. That law is based on nature, not on opinion. “‘Nature’ here means the condition of man as it actually is, within the cosmos. So the law based on this objective nature will be a set of general principles, providing a criterion for the laws of diverse communities” (xxix).