When a man means to give his attention to law (jus), he ought first to know whence the term jus is derived. Now jus is so called from justitia; in fact, according to the nice definition of Celsus, jus is the art of what is good and fair.

  1. Of this art we may deservedly be called the priests ; we cherish justice and profess the knowledge of what is good and fair, we separate what is fair from what is unfair, we discriminate between what is allowed and what is forbidden, we desire to make men good, not only by putting them in fear of penalties, but also by appealing to them through rewards, proceeding, if I am not mistaken, on a real and not a pretended philosophy.
  2. Of this subject there are two departments, public law and private law. Public law is that which regards the constitution of the Roman state, private law looks at the interest of individuals; as a matter of fact, some things are beneficial from the point of view of the state, and some with reference to private persons. Public law is concerned with sacred rites, with priests, with public officers. Private law has a threefold division, it is deduced partly from the rules of natural law, partly from those of the jus gentium, partly from those of the civil law.
  3. Natural law is that which all animals have been taught by nature ; this law is not peculiar to the human species, it is common to all animals which are produced on land or sea, and to fowls of the air as well. From it comes the union of man and woman called by us matrimony, and therewith the procreation and rearing of children ; we find in fact that animals in general, the very wild beasts, are marked by acquaintance with this law.
  4. Jus gentium is the law used by the various tribes of mankind, and there is no difficulty in seeing that it falls short of natural law, as the latter is common to all animated beings, whereas the former is only common to human beings in respect of their mutual relations .

Translation by Charles Henry Monro.